Overboring is hardly ever needed if the cylinder walls are ok, you really just need to check the piston to wall clearance and ring gap and go from there or....my personal opinion, buy the pistons and rings and bring them to Eisles or any competant machine shop and have them bore the block out to match the piston diameter as opposed to "general bore .20 or .25"....as pistons are NOT all the exact same bore...that way you know your getting the best seal possible, that's what I do...just my 2 cents...as well as many other engine builders...like Golden Eagle for example...