Butler Performance · Pontiac Tech

Pontiac Block Casting Identification

Every Pontiac V8 from the 287 to the 455 shares the same external block — so the casting number, date code, and a few physical tells are how you know what you actually have. Use the guide below to identify your block, then match it to the right rebuild and rotating-assembly parts.

326–455 · same outer block1955–1979Cross-checked vs Wallace Racing
Start Here

Identifying Your Block

1 · Find the casting number
1955–63: passenger side of the block. 1964–67: distributor pad (top rear), except 421s. March 1967 on: rear of the block, just behind cylinder #8. Clean off grime to read it — a phone photo helps.
2 · Read the date code
On the distributor pad: a letter = month (A=Jan … L=Dec), then the day (one or two digits), then a final digit = year. Example: F126 = June 12, 1966. 1967 only: J=September, M=December.
3 · Confirm with physical tells
Freeze plugs, transfer lug, displacement stamp, and the VIN derivative narrow the year and displacement when a casting number was shared across years. Details below.
Narrow It Down

Physical ID Tells

Freeze plugs
Two per side on 1955–1966 blocks. Three per side on 1967 and later. A fast first cut on era.
Transfer lug
A small pyramid at the rear, passenger side of the distributor hole. Present on 326/350/421/428/455; absent on 389/400. Exceptions: 1973 SD 455 has none, 1974 SD 455 has one.
Displacement stamp
1968–69 428s have “428” between the freeze plugs. From 1970 on, 350 / 400 / 455 is stamped front-left. There is no displacement stamp on 326, 389, or 421 blocks.
VIN derivative
1967 and later: a partial VIN is cast on the front, passenger side, near the timing cover — used to confirm a block is original to a given car.
Bottom-End Facts That Decide Your Parts
Main journal size is set by displacement — not year
3.00″ mains: 326 · 350 · 389 · 400.  3.25″ mains: 421 · 428 · 455. Rod journal (2.25″) and rod length (6.625″) are common across the family. The early 287–370 engines used smaller 2.5″–2.623″ mains. This is what determines crank, bearing, and balance selection.
2-bolt vs 4-bolt mains
Most Pontiac blocks are 2-bolt. Factory 4-bolt mains appear only on the 455 H.O./SD, 421 SD, and some Ram Air engines. Many 455 blocks were drilled for 4-bolt but shipped 2-bolt — confirm before you plan a high-output build.
Heads up: Pontiac automatics use the BOP/BOPC bellhousing pattern, not Chevy — most Powerglides and the 700R4 won’t bolt up without a dual-pattern bell or adapter.
Worked Examples

Reading the Date Code

J23
on casting 9773155 → J=October, day 2, year 3 = October 2, 1963 (a 1964-model 389).
F126
on casting 9782611 → F=June, day 12, year 6 = June 12, 1966. Note the two-digit day.
Blocks are cast a few months before the car is built, so the cast year may be one model-year earlier than the car.
Reference Tables

Casting Numbers by Year

1955–1963
  • Casting numbers are on the side of the block (passenger side) through 1963.
  • 1955–1963 blocks use stud-mounted (stud-oiled) rocker heads.
  • Two freeze plugs per side (1955–66).
YearCU INCasting #Notes
1955287518037
1956316521560
1957347523293
1958370528456
1959389532000
1960389536387
1961389538181
1961421538181SD
1962389538181
1962389542426SR
1962421538181, 548913late: 548913
1963326538211sources differ — see note ▲
1963389543680
1963421544988
1964–1966
  • 1964-and-up blocks moved to a block-mounted starter.
  • Casting number on the distributor pad (top rear), except 421s.
  • Date code now used — see “Reading the Date Code” above.
YearCU INCasting #Notes
19643269773153
19643899773155
19644219773157
19653269778840
19653899778789
19654219778791
19663269778840
19663899778789
19664219778791early
19664219782611late
1967–1969
  • Beginning March 1967, the casting number moved to the rear of the block, just behind cylinder #8.
  • Three freeze plugs per side (1967 and later).
  • VIN derivative cast on the front, passenger side, near the timing cover (1967+).
  • 1967 date-code exception: J = September and M = December that year only.
YearCU INCasting #Notes
19673269786339
19674009786133
19674289786135
19683509790079
19684009790071
19684009792506RA
19684289792968
19693509790079
19694009790071
19694009792506RA IV
19694289792968
1969303546313RA V short-deck
19694009792968RA V
1969428545887RA V
1970–1979
  • “428” is cast on 1968–69 428 blocks between the freeze plugs; from 1970 on, 350 / 400 / 455 is stamped on the front-left of the block (no stamp on 326/389/421).
  • 400 blocks with the 557 casting (e.g. 500557 / 568557) have thin main journals.
  • 1970-and-later blocks have 5 motor-mount holes (often untapped) for the 2nd-gen F-body; 1977–79 blocks dropped the rear mount holes entirely.
YearCU INCasting #Notes
19703509799916
19704009799914
19704009799914RA III · 4-bolt
19704009799915RA IV · 4-bolt
1970400481708RA V · 4-bolt
19704559799140
1971350481990
1971400481988
1971455483677HO
1971455485428late — verify HO ▲
1972350481990
1972400481988
1972455485428
19723664852124-bolt
1973350488986
1973400481988
1973455485428
1973455490132SD · 4-bolt
1974350488986
1974400481988
1974455485428
1974455490132SD · 4-bolt
1975350488986early
1975350500810late
1975400481988early
1975400500557late
1975455500813
1976350500810
1976400500557
1976455500813
1977301525934
1977400568557
▲ Verification notes. 1963 326 (538211): Wallace Racing and Butler list 538211; PontiacPower and some engine-code sheets list 548211 — confirm against the physical block. 1971 455 “late” (485428): some references class this as the H.O. casting, others as the standard 455; the 1971 455 H.O. is most often listed as 483677. Abbreviations: SD=Super Duty, RA=Ram Air, HO=High Output, SR=special.
Stroker Ranges

What Can I Build From It?

Once you know the block, here’s the displacement range Butler builds from each — click through to shop rotating assemblies sized to your block.

BlockMain JournalBuild Range (cu in)Shop
3263.00"336–382Shop »
3503.00"358–413Shop »
3893.00"395–480Shop »
4003.00"406–495Shop »
4213.25"427–489Shop »
4283.25"433–495Shop »
4553.25"462–503Shop »
Aftermarketvaries455–541Shop »
Not sure what you’ve got? Send us the numbers.
Photograph or note your block casting number and date code (heads too, if you have them) and our techs will confirm displacement, year, and what fits your build.
Keep Going

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Pontiac Blocks — Bore & Stroke Chart
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Reviving the Rocket — The Olds 403
The 403’s 4.351" bore and how it fits the 1977–79 Trans Am picture.
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Pontiac Engine Information
Reference overview of Pontiac V8 displacements and families.
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Internal vs External Balance
What your flexplate/flywheel must match once you know the block.
Read »
Rotating Assemblies & Stroker Kits
Shop assemblies by block once you’ve identified yours.
Read »
Casting and date-code data cross-checked against Wallace Racing, PontiacPower, Hagerty, Over-Drive Magazine, and the CarTech Pontiac crank guide, alongside Butler Performance build experience. Pontiac reused casting numbers across years and applications — always confirm with the date code and the physical tells above. When in doubt, send us the numbers.

Pontiac Blocks Casting Information

1955-1963

Blocks up to 1963 have side of block casting numbers

Up to 1963 have stud oiled heads
Year CU IN Casting #
1955 287 518037
1956 316 521560
1957 347 523293
1958 370 528456
1959 389 532000
1960 389 536387
1961 389 538181
1961 421 538181
1962 389 538181
1962 389 542426 (SR)
1962 421 538181, 548913 (late)
1963 326 538211
1963 389 543680
1963 421 544988

1964-1966

1964 and up now had block mounted starters

Block codes are were now dated ex.  Letter represents month, first digit day, second digit year

9773155 with code J23- October 2nd, 1963

9782611 with code F126- June 12th, 1966
Year CU IN Casting #
1964 326 9773153
1964 389 9773155
1964 421 9773157
1965 326 9778840
1965 389 9778789
1965 421 9778791
1966 326 9778840
1966 389 9778789
1966 421 9778791 (early)
1966 421 9782611 (late)

1967-1969

Beginning in 1967 casting numbers moved to the rear of the block just behind cylinder #8
Year CU IN Casting #
1967

326

 9786339
1967 400 9786133
1967 428 9786135
1968 350 9790079
1968 400 9790071
1968 400 RA 9792506
1968 428 9792968
1969 350 9790079
1969 400 9790071
1969 400 RA IV 9792506
1969 428 9792968
1969 303 546313
1969 400 RA V 9792968
1969 428 RA V 545887

1970-1977

400 blocks with 557 casting numbers have thin main journals.
Year CU IN Casting #
1970

350

 9799916
1970 400 9799914
1970 400 RA III 9799914 4-Bolt
1970 400 RA IV 979991 (5) 4-Bolt
1970 400 RA V 481708 4-Bolt
1970 455 9799140
1971 350 481990
1971 400 481988
1971 455 HO 483677
1971 455 485428 Late HO
1972 350 481990
1972 400 481988
1972 455 485428
1972 366 (485)212
1973 350 488986
1973 400 481988
1973 455 485428
1973 455 SD (490)132
1974 350 488986
1974 400 481988
1974 455 485428
1974 455 SD (490)132
1975 350 488986 Early
1975 350 500810 Late
1975 400 481988 Early
1975 400 500557 Late
1975 455 500813
1976 350 500810
1976 400 500557
1976 455 500813
1977 400 568557