Poppop,
I'm with GMCpanel. I don't know of any differences internally. However, there are some minor cosmetic differences, depending on what it came out of.
I have an early 70's 250 in one of my 52's. It has a long tube (oil filler) that I know wasn't on either of the 2 Nova's I've had. Almost like it would have been in a van???
Additionally, this engine has what appears to be a factory cast iron split exhaust manifold. However, it's the only one I've ever seen.
I was told by the PO that the engine came out of a 70's Ma-Bell truck he picked up an auction.
