GMC's are very much different that Chevy engines- - - -aluminum pistons instead of cast iron, different lubrication system, and a bunch of other stuff. Mostly, the cost to rebuild a GMC is several times what a similar rehab on a Chevy would cost. Pistons, oil pumps, and water pumps are particularly scarce and expensive for a GMC engine. The cast iron pistons in a Chevy 216 rust tight to the cylinder walls pretty regularly.
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!