Chevy didn't get stingy with their cast iron cylinder wall thickness until the mid-1970s. All the early stovebolt sixes and most 1950s and 60s small V8s will handle 60 over without problems. The early sixes handle 80 over as a matter of routine. Thinwall blocks came around in the 70s for both V8 and 6 cylinder engines. Ditto for cylinder heads- - - -don't get radical with a die grinder on the newer ones!
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!