The cylinder casting that BOLTS to the crankcase definitely rules out Chevy. Coincidentally, GMCs all the way up to the big 503 cubic inch from the mid-1950s had that same design. GMC was built to be rebuilt, repeatedly. Chevy was sort of a "one and done" production- - - -with limited overhaul capability.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!