Hey, Ive been working on cars for a while but mainly imports (japan and such), well ive been looking into building an old rolling camaro SS chassis that a friend sold me but didnt have an engine, until now, but i have no idea what it is...

It is in great shape and has been kept clean and free of rust.. this is the thing... it is still in the factory crate (which is def old, held together by solid wire spanning around the whole thing and bent into locking tabs where the lid locks closed), which is labled "general motors half engine 396921." i didnt look for any casting numbers yet but its brand new in the crate and im sure its the original crate because it was passed down to me in my family by a member who used to race professionally in the 70's... its def original still had the plastic on it.. came with two holly 4 barrel carbs and old (but also new) elbrock valve covers... not worried about the carbs yet just want to know what engine i have, any help appreciated! if i need to take it out and get castings i will, just wondering if anyone heard of this first...