Hy larryelvick, according to the parts book GM only offered pistons as large as .040" oversize. That being said in my experience .060" is the usual large size limit to reboring most engines. The newer engines with their thin wall castings cannot be bored even to .060" I have safely bored 265 V8 and 283 V8 blocks to .125", the last 261 rebuild I did for a customer was a 1955 - 62 block which was succesfully bored to .080" with no operating problems whatsoever. There is a new tool in the machine shops arsenal, sonic testing to check the thickness of the cylinder walls, hope that helps.
