Hello ! Tracking down my block, it looks like it is out of a B-Body 68' Pontiac. I believe that was Bonneville, Catalina, etc.. since it is a YC block code 9790071.

Question, how would I know what the factory bore was and if it was bored out ever ? I can measure the bore i.d. with a set of digital calipers, but wouldn't know what to compare it to. Also, is there an easy way to tell just by looking at it ??
Thanks.

Might want to look for any non-oem markings. Some machine shops will stamp the blocks for tracking purposes as well as what the bore out was.

Ok, thanks. I did notice looking at one of the piston tops, it said "Front" on it, maybe it had an arrow, but I think it maybe also said "std" which probably means standard bore ??

I believe original bore on a 400 is 4.12...

Thanks ! Thats what it measured with calipers. 4.125" Must be stock, makes sense. Looks like someone pulled this engine from a Catalina or Executive (1968) and put it in the bird. They did put a Holley Street Dominator intake, and double pumper Holley carb, along with headers (and believe to have a new cam in it). Other than that though, it would appear they left the rest stock. Probably was standard protocol for pimpin a car out in the 70's, along with N50's and wheel flares. No shag carpet on this one though !

4.120 is stock. Be sure to measure below the ridge.