Pontiac Block Casting.
1955 287 (288) 518037
1956 316 521560
The block casting number is located on the right side (passenger's side) of the engine block below the cylinder head surface and is centered between the freeze plug holes.
Pontiac V8 4 Barrel intake casting number.
55 278 (GMC 288 55-56) #521512
56 316 (GMC 316 55-56) #521570
They are located on the number 1 intake runner by the thermostat
The two intake are interchangeable. But like Bill said “none of the Pontiac-based GMC V8 engines came from the factory with a 4-barrel carb, so it could have been added later.
Rarity ?
Last edited by jimgmc; 08/20/2023 4:07 PM.
