Diesel Bombers - Boreing out the cylyinders?

Ok as some may know i cracked my 53 block, found an H.O. out of an 02. but i would have to bore it out to use it. So with that i decided to look for another. I traveled and 8hr trip yesterday to look at a block that a dumb ass swore up and down that it wasnt a "53". sent me pics but always seemed to dodge where the 53 was. I drove up there he said lets load it up, i said not to fast. went and looked it was a "53" :nope: and it already had a hair line crack in it. the guy almost died.:s:(Dumb ass). Any ways on that note i found one a little closer, im going to look at monday. But my question is that if i was to take that H.O. that i had and bored it out to 20 over, then what are the risks, Positive and negative. I want to know it all becuase I have been with out my truck for over a month and really want her on her feet again