Here’s the thing that surprises people: from the 326 to the 455, every traditional Pontiac V8 uses essentially the same external block and the same ~10.24" deck height. Displacement comes from bore and stroke, not a bigger casting — which is exactly why a single block can be built into so many cubic-inch combinations.

• Smallest of the 3.00" main-journal blocks; thin cylinder walls limit overbore — sonic-check before going past +.040.
• A budget-friendly stroker base: a 4.00" or 4.25" crank takes it well past stock cubes.

• Small-bore 3.00" main block; cylinder walls are the limit, so confirm wall thickness before a big overbore.
• Stroking to 4.00"–4.25" is the popular way to wake one up without chasing bore.

• The classic GTO block. 3.00" mains, 3.75" stock stroke.
• A 4.25" or 4.50" crank turns a 389 into a 447–482 cu in torque monster.

• The most popular Pontiac stroker base — 3.00" mains, plentiful, and responds well to a 4.25" crank for a 461.
• 557-casting blocks (1975–76 / late blocks ending in 557) have thinner main webbing — limit to a 4.00" stroke and under ~500 hp.
• Early 1967 400s can have a deep 389/421-style cylinder chamfer; if it's deeper than .250", a lowered-ring piston is needed.
• The 460-467 stroker kits are the Butler go-to for builds wanting more Torque and HP. 

• First of the big 3.25" main-journal blocks; 4.00" stock stroke.
• Plenty of room to stroke to 4.25"–4.50" for 447–489 cu in.

• Big-bore 3.25" main block with a 4.00" stock stroke — a strong, under-rated stroker base.
• A 4.25" crank lands it near 460 on first rebuild; 4.50" pushes toward 495.

• The largest factory Pontiac — 3.25" mains and the longest factory 4.21" stroke.
• Already huge from the factory; a 4.50" crank takes it past 500 cu in.

Need more than a factory block can safely give? Aftermarket Pontiac blocks support 455–541 cu in with thicker decks, priority main oiling, and four-bolt mains for high-horsepower and power-adder builds. 3" Main Journals with options on standard or big cam tunnel (50mm-55mm) and standard or big lifter bores (.903)

Commonly IAII Blocks configurations
Cast Iron- 4.350 bore, Standard Cam, Standard Lifter
Cast Iron- 4.350 bore, Large Cam, Large Lifter
Cast Iron- 4.250 bore, Large Cam, Large Lifter
Cast Iron- 4.150 bore, Standard Cam, Standard Lifter
Aluminum- 4.250 bore, Large Cam, Large Lifter
Aluminum- 4.250 bore, Large Cam, Standard Lifter

All bores are rough bored to .005 under. The final hone nets these listed bores.
Large lifter blocks can have standard size .842 lifter bushings installed .