How to Identify a Pontiac, Oldsmobile and Buick V8 Engine

Casting numbers say which part a block or head is; the stamp and date code say when and where the engine was built. Start with the VIN for what the car left the factory with, then check the engine itself, since engines get swapped.

Where the numbers are and what they mean

Head date 1963 — 1963 Pontiac 389/421: left and right heads are the same casting; the cylinder-head casting date is at the right front corner of the right head and the left rear corner of the left head.
Engine stamp pad — Engine (application) code stamped on the front of the passenger-side bank, just below the head, with the 6- or 7-digit motor unit number above it (not the VIN). 2-letter codes began in 1965 (1962-64 used number+letter codes like 01A). Rule of thumb: W = manual, Y = automatic, most Z = automatic, X = both. 1967+ blocks also carry a VIN derivative on the front passenger side.
Unit number 1969 72 — 1969-72 Olds V8 (factory service manuals in the 4-4-2 kits): the engine unit number is stamped on the engine oil fill tube, with the engine code tape installed directly above it; the 1969 and 1971 AMA forms give the engine number (VIN derivative) location as the left front of the engine block.
Engine stamp pad — 1968 and later: VIN derivative stamped on a machined pad on the front driver side of the block just below the head (below No. 1 plug), format 3 + year digit + plant letter + last 6 of VIN (e.g. 38M203456; 3 = Oldsmobile). An engine unit number/ID is also stamped on the front of the oil filler tube (factory: 1969 W-31 "9XXXXXX", 1970 W-30 "DXXXXXX"). 1964-67 engines: unit number on the front pad of the right-hand head, prefix T/W (330) or V (400), suffix letter for compression.
Engine stamp pad — Buick 350 (1969-70 factory specification forms): the engine number is on the LEFT cylinder bank at the front, on top of the block just below the head.
Engine stamp pad — Buick 400/430/455 (1969-70 factory specification forms): the engine number is at the REAR of the RIGHT side - 'Right Cylinder Head at Rear on Boss' (1969 GS 400, 1970 GS 455) / 'Top of Right Cyl. Block at Rear' (1969 Wildcat, Electra 225, Riviera 430).

Cylinder head casting numbers

Casting	Years	Used on	Chamber (cc)	Valves (in)	Notes
400370 (code D)	1968-1969	400 and 455 W-30 and H.O. (non-A/C 1968 H/O, all 1969 H/O)	69.75 (FAQ); factory 1969 W-30 400: minimum head volume 69.75 cc	2.072/1.625 (FAQ); factory 1969 W-30 max 2.077/1.630	Factory 1969 W-30 sheet gives head part 230612, casting 400370
403686 (code E)	1970	455 (except W-30)	77 or 80	2.000 (2.072 Toronado/442)/1.625	valve rotators on all valves
397742 (code 5)	1968-1969	350 (all, incl. W-31)	64 (FAQ); factory 1969 W-31 minimum head volume 60.58	1.875/1.562 (W-31 1.995/1.624) (FAQ)	Factory 1969 W-31 sheet: head part 230619, casting 397742
403859 (code 6)	1970	350 (all, incl. W-31)	64	1.880 (W-31 1.995)/1.567 (W-31 1.624)	Factory 1970 W-31: head part 230895, casting 403859

How to tell a Pontiac 350 from a 400 vs 455

Bore and stroke (1972 factory spec): 350 = 3.8750-3.8774 x 3.746-3.754 in; 400 = 4.1200-4.1224 x 3.746-3.754 in; 455 = 4.1510-4.1534 x 4.214 in. Measuring the bore separates 350 from 400/455; the 455 has the long 4.21 in stroke.
Chamber size by displacement (1972 factory): 350 89.76 cc; 400 95.61 cc (4-bbl) / 96.36 cc (2-bbl); 455 111.89 cc (4-bbl) / 112.64 cc (2-bbl).

How to tell a Olds 455 from a 400 (big block)

Bore and stroke (factory): 1968-69 400 = 3.870 x 4.250 in; 1970 455 = 4.125 x 4.250 in. The 1968-69 400 shares the 455 stroke and differs only in bore.

How to tell a Buick 350 from a Chevrolet 350

Bore and stroke: Buick 350 = 3.800 x 3.850 in (factory 1970 spec), a smaller bore and longer stroke than the Chevrolet 350.
Intake/exhaust valves 1970 Buick 350 (factory): intake head dia. 1.870-1.880 in, exhaust 1.495-1.505 in.

How to tell a Buick 400 from a 430 vs 455

455 bore x stroke 4.3125 x 3.900 in (factory 1970).
1970 Buick 455 valves (factory): exhaust head dia. 1.620-1.630 in; intake about 2.00 in (OCR reads "2 005").