Depends on which Pontiac engine you are referring to. Any GM engine 400 cubic inches and under are considered a small block with two exceptions. The 396 is a big block and there were certain 400's that are big blocks. Two versions of the 400 were built.
WRONG. All Pontiacs from 326-455 are the same size block externally. The only major difference is that the 326, 350, 389, and 400 have a 3" main bearing size. The 421, 428, and 455 are 3.25" mains. Now...if you are talking about comparing a Pontiac block to say a Chevy block....the Pontiac is larger than a small block and slightly smaller than a big block.
