so, i dropped my block off at the machine shop on monday to be bored out to 3.903. the shop is going to sonic test it before they bore. my question is, what is a safe cylinder wall thickness? the shop is known for building roundy round engines and has received many rewards/trophies for their work, but they seem to be a little wet behind the ears when i brought them my block. he's supposed to call me after he sonic tests it and i would like to be confident in giving him the go ahead.