Cubic Inch Style Year Produced Bore Stroke
223.4 L-Head Straight 8 1933-35 3 3/16 3 1/2
208 L-Head Straight 6 1935-36 3 3/8 3 7/8
232.3 L-Head Straight 8 1936 3.25 3.50
222.7 L-Head Straight 6 1937-40 3 7/16 4.00
248.9 L-Head Straight 8 1937-49 3.25 3.75
239.2 L-Head Straight 6 1941-54 3 9/16 4.00
268.4 L-Head Straight 8 1950-54 3 3/8 3.75
194.5 (1/2 389) INDYFOUR 1961-63 4.06 3.75
215 Overhead Valve 6 1964-65 3.75 3.25
230 Overhead Cam 6 1966-67 3.87 3.25
250 Overhead Cam 6 1968-69 3.88 3.53
287 V-8 1955 3.75 3.25
316 V-8 1956 3.94 3.25
347 V-8 1957 3.94 3.56
370 V-8 1958 4.06 3.56
326 V-8 1963-67 3.781 3.750
350 V-8 1968-77 3.875 3.750
389 V-8 1959-66 4.063 3.750
400 V-8 1967-79 4.120 3.750
421 V-8 1961-66 4.094 4.000
428 V-8 1967-69 4.120 4.000
455 V-8 1970-76 4.150 4.210

This is a quick block ID for junk yard hunting, etc. You must find the date code at the back LH side of the block first. The letter is the month, next 2 digits are the day and the last digit is the year. Here are 2examples:

A249 code "XE"
A = January - 24 is the 24th day - and 9 is 1969
The block is a 69 428.

Another example is:

K109 "WA"
K = October or November - 10th day - 9 = 1969
The block is a 70 455 4 bolt.
These motors usually have a large "70" at the rear of the block.

*Note - blocks with only 2 mounting holes or pads (for the motor mounts) per side is from 1969 and older blocks with 5 or 3 mounting holes or pads (for the motor mounts) per side is from 1970 and newer blocks with 2 freeze plugs per side is 1966 and older blocks with 3 freeze plugs per side is 1967 and newer certain blocks for 4 bbl carb usage have scallops in the cylinders at the deck for unshrouding the intake valves. Most 1967 and earlier blocks place these scallops at approx 4 o'clock and 8 o'clockwhile 1968 and newer blocks place the scallops at 3 o'clock and 6 o'clock . Early 2 bbl blocks and most newer blocks did not have any scallops.

400 Engine Codes
Year Model Codes
1967 GTO XM XL WT WW YS XE WS WV YZ YI (RAM AIR) XS YR XP
1967 FIREBIRD WZ WU YT (RAM AIR) WQ XN WI
1967 FULLSIZE XA XB WA WB WM WN YA YB YC XV YD XU YU YV XC YE XW YF XX YX WD XT WE WY XY XZ YL XH XJ WF
1968 FULLSIZE YA XA WA WB YC ZR YE YF XZ XH
1968 GTO XM WT YS (400 HO) WS YZ (RA I) XS XP (RA II) WY XW
1968 FIREBIRD WZ YT (400 HO) WQ YW (RA I) WI XN (RA II) WU XT
1969 FIREBIRD WZ YT (RA III) WQ YW (RA III) WH XN
1969 GTO WT YS XM XX (RA III) WS YZ (RA IV) WW XP
1969 FULLSIZE WA WD YA YB WB WE YC YD XZ WX XH YF WA WD YA YB WB WE YC YD
1970 FULLSIZE WE YD YB XZ WX XH
1970 GTO & FIREBIRD XX XV WT YS (RA III) WS YZ (RA IV) WW XP
1971 FULLSIZE WS XX YS
1971 GTP, GP, & FIREBIRD XX WT WK YS
1972 ALL YX YZ ZX WS WK YS YT
1973 ALL YP ZK Y4 YX Y1 ZX YZ YT XK ZN WS YF WP Y6 YG YN ZS YY XX X5 Y3 YS XN
1977-79 T/A 6.6 (W72) OPTION casting number 481988 XX is cast on the valley area and externally
428 Engine Codes
Year Codes
1967 WG YY YH Y2 XD WJ XK YK Y3
1968 WG YH WJ YK
1969 YL YH WG XK XE XJ WJ YK WF XF WL XG
455 Engine Codes
Year Model Codes
1970 FULLSIZE YH - 2 BOLT WG XF - 4 BOLT
1970 GTO WA YA YC - 4 BOLT
1971 FULLSIZE WJ YC WG YG - 2 BOLT
1971 OTHERS HO (4 BOLT) WL WC YE
1972 2 BOLT YH YC YA ZH
1972 4 BOLT (HO) WM YB WD YE 4 BOLT (HO) WM YB WD YE
1973 YK X7 YD XM WW WT YC XE YA XL ZC ZA (SD) ZJ XD
1974 Y9 Y4 Y6 A4 Z4 Z6 YY YU YX AU ZU ZX YW ZW YR (SD) W8 Y8
1975 YW YU ZU ZW WX
1976 Y3 Y4 Z3 Z4 Y8 ZB WX

Service Replacement (SR) blocks do not always have a code stamped on the front of the engine. They do, however, usually have a casting number. This casting number is usually on the RH side of the rear portion of the block - where the transmission bolts up. 
Here they are:

400
Year Numbers
1967 9786133
1968 9790071
1968 RAM AIR 9792506
1969 9790071
1969 RAM AIR IV 9792506
1970 9799914
1970 RAM AIR IV 9799915
1970-74 481988
1975 488986 (early) 500557 (late)
1976 500577
1977-79 568577
1978-79 (T/A 6.6) 481988 xx
428
Year Numbers
1967 9786135
1968-69 9792968
455
Year Numbers
1970 9799140
1971 483677 (early) 485428 (late)
1972-74 485428
1973-74 (SD) 490132
1975-76 500813
Year Application Casting Valves CC or CR Notes
1967 400 2bbl/4bbl 61 2.11/1.77 75 PRESSED IN STUDS – UNIQUE OPEN CHAMBER
1967 400 4bbl RA I 97 2.11/1.77 72 SCREW IN STUDS – TALLER VALVE SPRINGS- D PORT
1967 400 4bbl RA I 997 2.11/1.77 72 SCREW IN STUDS – TALLER VALVE SPRINGS- D PORT
1967 326 2bbl 140 1.96/1.66 9.2 CR PRESSED IN STUDS – D PORT
1967 326 4bbl 141 1.96/1.66 10.5 CR PRESSED IN STUDS – D PORT
1967 400 2bbl 142 1.96/1.66 - PRESSED IN STUDS – LOW COMPRESSION- D PORT
1967 400 2bbl/4bbl 143 1.96/1.66 75 PRESSED IN STUDS – D PORT
1967 400 std, HO 670 2.11/1.77 72 SCREW IN STUDS – DUAL VALVE SPRINGS- D PORT
1968 400 2bbl 14 1.96/1.66 90 PRESSED IN STUDS –D PORT (B & G BODY)
1968 400 2bbl/4bbl 15 1.96/1.66 75 PRESSED IN STUDS –D PORT (B & G BODY)
1968/69 400 std, HO 16 2.11/1.77 72 SCREW IN STUDS – DUAL VALVE SPRINGS- D PORT
1968 350 2bbl 17 1.96/1.66 80 PRESSED IN STUDS – D PORT (A & F BODY)
1968 350 4bbl, HO 18 1.96/1.66 68 PRESSED IN STUDS – D PORT (A & F BODY)
1968 400 4bbl, RAI 31 2.11/1.77 72 SCREW IN STUDS – DUAL VALVE SPRINGS- D PORT ( A & F BODY)
1968/69 400 62 2.11/1.77 75/72 SCREW IN STUDS – DUAL VALVE SPRINGS- D PORT
1968 400 RAII 96 2.11/1.77 71 SCREW IN STUDS – DUAL VALVE SPRINGS- D PORT
1969 400 2bbl 45 1.96/1.66 8.6 CR PRESSED IN STUDS – LOW COMPRESSION- D PORT (B & G BODY)
1969 400/428 2bbl/4bbl 46 1.96/1.66 10 CR PRESSED IN STUDS – HIGH COMP.- D PORT 30 OR 45 SEAT ANGLE (B & G BODY)
1969 350 2bbl 47 1.96/1.66 80 PRESSED IN STUDS – D PORT (A & F BODY)
1969 350 4bbl, HO 48 2.11/1.77 69? SCREW IN STUDS – DUAL VALVE SPRINGS- D PORT
1969 400 MT, RA, HO 48 2.11/1.77 72 D PORT RAIII
1969 400 RAIV 722 2.11/1.77 71 SCREW IN STUDS- DUAL VALVE SPRING- ROUND PORT
1970 350/400 2bbl 11 1.96/1.66 85 PRESSED IN STUDS- D PORT
1970 400 MT, RA 12 2.11/1.77 72 D PORT
1970 400 13 2.11/1.77 72 D PORT
1970 455 2bbl/4bbl 15 1.96/1.66 87 PRESSED IN STUDS – D PORT (B & G BODY)
1970 400 2bbl/4bbl 16 1.96/1.66 10.1 CR PRESSED IN STUDS – D PORT
1970 455 HO 64 2.11/1.77 87 D PORT
1970 400 RAIV ROUND PORT 614 2.11/1.77 71 SCREW IN STUDS – DUAL VALVE SPRINGS
1971 455 66 2.11/1.77 114 PRESS IN STUDS
1971 350 2bbl 94 1.96/1.66 90 SCREW IN STUDS – D PORT
1971 400 4bbl 96 2.11/1.77 96 SCREW IN STUDS – DUAL VALVE SPRINGS – D PORT
1971 455 2bbl 98 1.96/1.66 114 PRESSED IN STUDS – D PORT
1971 400 2bbl 99 1.96/1.66 96 PRESSED IN STUDS – D PORT
1971 455 HO ROUND PORT 197 2.11/1.77 111 SCREW IN STUDS- DUAL VALVE SPRINGS
1972 455 HO ROUND PORT 7F6 2.11/1.77 111 SCREW IN STUDS- DUAL VALVE SPRINGS
1972 350 2bbl 7H1 1.96/1.77 90 PRESSED IN STUDS- 45/45 DEGREE SEATS
1972 400 2bbl 7J2 1.96/1.77 96 PRESSED IN STUDS- 45/45 DEGREE SEATS
1972 400 2bbl 7K3 2.11/1.77 96 SCREW IN STUDS – DUAL VALVE SPRINGS- D PORT
1972 455 2bbl 7L4 1.96/1.77 112 PRESSED IN STUDS – 45/45 DEGREE SEATS
1972 455 4bbl 7M5 2.11/1.77 114 -
1973/74 455 SD ROUND PORT 16 2.11/1.77 111 SCREW IN STUDS – DUAL VALVE SPRINGS
1973/74 350 46 1.96/1.66 96 PRESS IN OR SCREW IN STUDS
1973/74 350 4C-5H 1.96/1.66 96 PRESS IN OR SCREW IN STUDS
1973/74 400 4C-8H 1.96/1.66 98 PRESS IN OR SCREW IN STUDS
1973/74 455 4X-1 (H) 2.11/1.66 112/114 PRESS IN OR SCREW IN STUDS
1973/74 400 4X-3 (H) 2.11/1.66 98 PRESS IN STUDS
1973/74 400 4X-4 (H) 2.11/1.66 98 PRESS IN STUDS
1973/74 400 4X-7 (H) 2.11/1.66 98 SCREW IN STUDS- DUAL VALVE SPRINGS
1975 350 4bbl 5C-4 2.11/1.66 93 SCREW IN STUDS
1975 350 5C-9 2.11/1.66 93 A.I.R.
1975 400 4bbl 5C-8 2.11/1.66 101 SCREW IN STUDS- 30/45 DEGREE SEATS
1975 350/400 4bbl 5C-7 2.11/1.66 100 SCREW IN STUDS
1975 455 5C-6 2.11/1.66 124 SCREW IN STUDS
1975 455 4bbl 51 2.11/1.66 124 SCREW IN STUDS- 30/45 DEGREE SEATS
1975/76 455 4bbl 6H 2.11/1.66 124 SCREW IN STUDS- 30/45 DEGREE SEATS
1975/76 350 6S-9 2.11/1.66 93 -
1975/76 400 6S-7 2.11/1.66 100 -
1975/76 455 6S-6 2.11/1.66 124 -
1975-79 350/400 6X-4 2.11/1.66 98 SCREW IN STUDS- DUAL VALVE SPRINGS- D PORT
1975-79 400/455 6X-8 2.11/1.66 101 SCREW IN STUDS- DUAL VALVE SPRINGS- D PORT

What are you looking for?