One of the big problems encountered when rebuilding GMC engines is the very difficult task of locating suitable pistons. I have found a few sources for metric diameter pistons for Japanese Diesel engines (forklifts, etc.) that can be adapted for use in GMCs. They're available and affordable from various Ebay vendors. For instance: these pistons can be fitted to a 302 GMC with a little creative metal butchering:

www.ebay.com/itm/156414489925?

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!