Some of the early blocks are supposed to be able to go to 4.375", which is .125" over stock. The largest I have run is 4.350" in a truck block with the 4.250" crank it was 505 cubic inches. I ran first an 8-71 blower on it, and later a Gentry turbo setup, up to 15 lbs boost, perhaps 1000 HP with no block issues.
To be safe, the block should be sonic checked for cylinder wall thickness I would think. It's very common to go to .060" over stock (4.310"). Can't tell you exactly how many bores since there are some weird piston sizes made, maybe .020" , .040" and .070" , besides the "normal" .030" and .060", and then as I mentioned even .100 and .125" over
