If you have the engine tag still attached to the engine - just in front/below the thermostat housing - or perhaps the original engine number in the log book then the following should help you determine which engine you have.

For Metro units, see 'Engine - Metro identification data'.

Original engine identification numbers

850cc
8A           Austin up to 25000
8MB        Morris up to 25000
8AM        Austin & Morris 25000 onwards
8AH        Austin & Morris Automatic
8AJ        Austin & Morris closed circuit breathing
8AK        Austin & Morris automatic with closed circuit breathing
8WR       Wolseley Hornet & Riley Elf
8AC        Moke
85H/101 All variants 1969 onwards

Note: third suffix letter denotes compression type, L = Low, H = High, e.g. 8AM/U/H101 denotes high compression.

998cc
9WR             Wolseley Hornet & Riley Elf Mk2, pre closed circuit breathing
9AD              Austin, Wolseley Hornet & Riley Elf Mk2 with remote type gearbox and closed
                       circuit breathing
9AE               Wolseley Hornet & Riley Elf Mk3
99H/-/101 on Wolseley, Riley, Mini 1000, Clubman1000 1970 onwards and Mk3 with dished
                       piston
99H/791        Mini 1974 onwards with dished piston
99H/997        1980 onwards A+ block, flat top psitons, economy fitment with 2.95 final drive
99H/A97P     A+ block with dished pistons, pre-A+ gears, 3.44 final drive & 12-inch wheels

 
998 A+ block with centre locating tang in main cap, 1985 onwards
Flat top piston with circlip wrist pin retention
99H/B81      Up to engine number 127431
99H/C20      Up to engine number 105023
99H/997       From engine number 127422 with 2.95 final drive
99H/A35P

Flat top piston with press fit wrist pin
99H/B81     From engine number 127432
99H/C20     From engine number 105024
99H/D80   

Flat top pistons with press fit wrist pins, Lead-free cylinder head
99H/G30 or G32 or G33  
99H/F15 or F16
99H/E20 or E21
99H/D81
LBB10089

Dished pistons with circlip wrist pin retention
99H/B83P     Up to engine number 102908
99H/B84P     Up to engine number 100216

Dished pistons with press fit wrist pin
99H/B83P     From engine number 102909
99H/B84P     From engine number 100217

Dished pistons with press fit wrist pin, Lead-free
99H/G31
99H/E22
LBB10175

 
1100cc (1098cc)
10AMW/Ta       Clubman Estate and Austin 110 (ADO16 shape)
10H791               Clubman saloon
10H/-/H              All Austin 1100 2 & 4 door derivative Saloons (ADO16 shape)
10GR/Ta/H        MG1100 (ADO16 shape)
10GRB/Ta/H     MG1100 & Wolseley 1100 (ADO16)
10V/Ta/H           Vanden Plas 1100 (ADO16 shape)

 
997 Cooper
9F/Sa/H101 to 2637 except 19201 to 20410 (became 1070S)

998 Cooper January 1964 onwards)
9FA/Sa/H     Mk1 Austin pre closed circuit breathing
9FD/Sa/H     Mk1 Morris up to engine number 1934, all Austin Mk2 closed circuit breathing and
                       Morris Mk2 from engine number 1935-33660 with closed circuit breathing
9FD/Xe/H     4 syncro gearbox introduced
99/-/H            Last of manufacture 1969

 
Cooper S variants
970cc
9F/Sa/X         Engine numbers 29001-29003 with Tecalamit filter
9FD/Sa/X      Closed circuit breathing introduced with Tecalamit filter
9FE/Sa/X      Closed circuit breathing, oil filter with oil light switch introduced
9F/Sa/X        Engine numbers 29039-30029 Purolator oil filter with oil light switch and closed
                       circuit breathing
1070cc
9F/Sa/H       Engine numbers 26501 to 33660 and 19201 to 20410
9FD/Sa/H    Engine numbers 33661 to 33948 with closed circuit breathing and oil light switch in
                     oil filter head
1275cc
9F/Sa/Y        Engine numbers 31001 to 31504 pre closed circuit breathing with Purolator oil filter
9FD/Sa/Y    Closed circuit breathing with oil light switch on filter housing after engine number
                     32178
9FE/Sa/Y    Closed circuit breathing with oil light switch on Purolator filter housing and piston
                    design change
9F/Sa/Y       From engine number 32378 onwards, cosed circuit breathing with Purolator filter
                    with oil light switch, Aeg510 camshaft introduced at engine number 40006, cross-
                    drilled EN40Bcrank at engine number 42730 and metal dipstick tube at engine
                    number 42548 onwards
12H397       Cooper S Mk3 with dynamo, negative earth and Tuiftrided EN16T crankshaft
12H398       Cooper S Mk3 with alternator, negative earth and Tuftrided EN16T crankshaft

Note: Only Cooper S engines with prefix '9F' had EN40B forged steel, nitrided crankshafts. All other A-series engines had EN16T steel crankshafts which were only Tuftrided on Mk3 'S' and Austin 1300GT (ADO16) and were stamped 12G1683.

 
1275cc, Solid wall block (no tappet chest covers)
12G/Ta/H        ADO17 shape Wolseley, Riley, MG & Vanden Plas fitted with S rods
12H379           1275GT with dynamo, negative earth, electric fuel pump and remote type gearbox
12H380           1275GT with alternator, negative earth, electric fuel pump and remote type  gearbox
12H389           1275GT with dynamo, negative earth, mechanical fuel pump and remote type gearbox
12H390            1275GT with alternator, negative earth, mechanical fuel pump and remote type gearbox
12H706            1275GT with alternator, negative earth, mechanical fuel pump and rod changegearbox
12H397            Cooper S Mk3 with dynamo and negative earth
12H398            Cooper S Mk3 with alternator and negative earth
12H/-/             1275 Austin ADO16 & Allegro
12H610/635     Innocenti Mini with duplex cam drive gears and 11-stud head
12H719/832     Innocenti Mini with simplex cam drive gears and 11-stud head

1275cc, 1990 onwards (12A numbers)
12A/2A            Carburrettor type
12A/2B            Carburrettor and catalyst type
12A/2D            SPi (Single Point injection - Tbi, throttle body injection) with 9.4-1 CR
12A/E              SPi (Tbi - throttle body injection) with 10-1 CR
With the following suffixes:
F53                  10.0-1CR, 3.105 final drive, catalyst, oil cooler
F75                   9.4-1CR, SPi, 3.105 final drive, closed loop catalyst
F76                   9.4-1CR, automatic with closed loop catalyst
F77                  10.0-1CR, SPi Cooper, 3.2 final drive, closed loop catalyst
G01                  10.0-1CR, 3.105 final drive, catalyst, no oil cooler
G03                  9.4-1CR, 3.105 final drive, catalyst, May 1992 onwards
G04                  9.4CR, 2.76 final drive, catalyst, French only spec
G05                  9.4-1CR, automatic with catalyst

 
Factory replacement engine reference numbers (i.e. New, and Gold and Silver Seal units)
8G28             850cc - Oil feed to primary gear type crank with 1.375-inch tail shaft
8G35              850cc - Deva bush conversion type crankshaft with 1.375-inch tail shaft
8G45              850cc - Gold Seal, 1.5-inch self oiling primary gear/crankshaft type
GSE1101E     850cc - Gold Seal unit
RKM1101E   850cc - Silver Seal unit
BHM1307E   850cc - Gold Seal unit, 85H prefix replacement
8G18              997cc Cooper - Oil feed to primary gear type crankshaft
8G29             997cc Cooper - Deva bush type primary gear and crankshaft
8G36             997cc Cooper - Oil feed converted primary gear and crankshaft
8G33             998cc Cooper - Fitted with 28G193 (12G202) cylinder head
8G40             998cc Cooper - 28G222 (12G295)cylinder head introduced
8G42             998cc Cooper - Closed circuit breathing rocker cover and side plates
8G49             998cc Cooper - Purolator oil filter with oil light switch introduced
GSE1103E    998cc Cooper - Gold Seal unit, was RKM1120E Silver Seal
RKM1103E   998cc Cooper - Silver Seal unit
8G57              998cc - New from 1969 and exchange for all pre-A+ up to 1981
GSE1102E     998cc -Gold Seal unit, was RKM1119E Silver Seal unit, pre-A+ up to 1981
RKM1102E   998cc - Silver Seal unit, pre-A+ up to 1981
RKM1119E   998cc - Silver Seal unit, replaced by RKM1102E, pre-A+ up to 1981
BHM1232     998cc - Low compression dished piston, CAM6267 camshaft, early cylinder head
                              and crankshaft main bearings with side locator tang, A+
BHM1377     998cc - High compression flat top piston, CAM4717 camshaft, early cylinder head
                              and crankshaft main bearings with side locator tang, A+
BHM1458     998cc - Low compression piston, CAM6267 camshaft, late A+ cylinder head and
                              crankshaft main bearings with central locator tang, A+
BHM1460    998cc - High compression press-fit wrist pin piston, CAM4717 camshaft, late A+
                             cylinder head and crankshaft main bearings with central locator tang, A+
LBB10089    998cc - Low compression press-fit wrist pin piston, CAM6267 camshaft, lead -
                             free late A+ cylinder head and crankshaft main bearings with central
                             locator tang, A+
8G156E       1100cc - Clubman, Special and Austin 1100 (ADO16)
RKM1150E   1100cc - Silver Seal unit for Clubman and Special
RKM1151E   1100cc - Silver Seal unit for Clubman and Special
BHM1042     1100cc - New and Gold Seal units for Clubman and Special, 1974-1980
BHM1229     1100cc - New and Gold Seal units for Clubman and Special, A+ Block, 1980 on
8G38            970cc - Gold Seal unit, pre closed circuit breathing, Cooper S
8G41            970cc - Gold Seal unit with closed circuit breathing sideplates, Cooper S
8G46            970cc - Gold Seal unit withoil light switch in filter housing, Cooper S
8G133          1070cc - Gold Seal unit, pre closed circuit breathing, Cooper S
8G153          1070cc - Gold Seal unit with closed circuit breathing side plates, Cooper S
8G145          1275cc - Pre closed circuit breathing unit, Cooper S
8G154          1275cc - Closed circuit breathing side plates unit, Cooper S
8G155          1275cc - Oil filter housing with oil pressure light switch, Cooper S
8G174          1275cc - Fitted with AEG510 camshaft, Cooper S
38G464        1275cc - Introduced in 1970, most of which were fitted with EN16 Tuftrided
                                crankshaft
8G200         1275cc - New and Gold Seal units Clubman 1275GT
38G527       1275cc - New and Gold Seal units for engine numbers prefixed 12H706, 12H707 &
                              12H831 for Clubman 1275GT
RKM1130E   1275cc - Silver seal unit, was RKM1112E, for Clubman 1275GT, pre-A+
RKM1152E   1275cc - Silver Seal unit for Clubman 1275GT, pre-A+
RKM1112E   1275cc - Silver Seal unit for Clubman 1275GT, pre-A+
BHM1220     1275cc - A+ unit for Clubman 1275GT
8G199E          1275cc - Gold Seal unit with Duplex cam drive gears for 1300GT (ADO16) and
                                Innocenti 1300, 11-stud cylinder head
38G559E        1275cc - Gold Seal unit with Simplex cam drive gears for engine numbers prefixed
                                12H719 and 12H832, for 1300GT (ADO16) and Innocenti 1300, 11-stud
                                 cylinder head
GSE1109E     1275cc - Gold Seal unit for 1300GT (ADO16) and Innocenti 1300, 11-stud cylinder
                                head
RKM1133E    1275cc - Silver Seal unit for 1300GT (ADO16) and Innocenti 1300, 11-stud
                                 cylinder head
BHM1209E    1275cc - Gold Seal unit, replaced all Innocenti 1300 engines from engine numbers
                                prefixed 12H610, 12H635 and 12H832

Notes:
All engines pre-fixed with 'GSE' or 'RKM' were of UNIPART origin when BL split its parts organisation.

'E' at the end of a part number denotes it is a reconditioned, service unit only (basic engine assembly with no ancillaries).

'N' at the end of a part number denotes a brand new unit.