just boring wont give to much in gains if any. it can cause overheating if the cylinder walls are to thin. i believe a 302 with a .30 or .40 bore is a 306 but not 100% on that. I wouldnt take a 302 over .40 personally unless it was an older 70's block
if you have to I would try, and get a core block from the junk yard that hasn't been bored yet if it was me. 40 is the max I would consider on a 302 block without sonic testing and even then I would really look into a new block it's not like they are rare or anything like that.
The one that says it cannot be done should never interrupt the one that is doing it
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