the two letter engine code is located on the front passenger side of the block, but from your photos it looks to be pretty heavily painted over, so you might have to scrape it off a bit to see it better. With that, along with the casting number found on the back of the block by the distributer, you can look up the codes on this website to determine year and specs...Thanks O52. Those numbers aren't that easy to get to. I'll see if can get them. I think the intake casting number is for a 1970 400 ci engine.
The Rochester Quadrajet carb # is 7028268 which belongs to a 1968 400/400 H.O. I installed a HEI distributor and got the car running. The carb is bad, it won't idle and needs to be replaced or rebuilt. Given those 2 things, I'm thinking it's a 400 ci engine.
Those numbers aren't easy to access or read. I will try again. TY66_Lemans. You’ve probably heard by now that Pontiac doesn’t have a Big Block or a Small Block engine. External dimensions pretty much stayed the same from the 50’s till the last day of production. This means that Pontiacs have unparalleled “swappability” of heads, blocks, manifolds, etc.
To find out what you have, really, you need to check the engine casting number by the distributor AND the head casting numbers on top of the center two exhaust ports.
Pontiacs left the factory with (essentially) flat top pistons, so compression ratio (CR) is determined by the cylinder head combustion chamber volume and the displacement of the short block.
Factory parts can be used to build engines with a CR from 6:1 to 14:1. A 1967 HO 326 was 250 HP; a 1975 455 was 200 HP! The biggest difference between 1967 and 1975 was Compression Ratio.
So, run your numbers and see what you have!