I didnt ahve to clearance any at all on my iron 6.0 block for my 4.100 stroke. The LS1 block needs ALOT of clearancing on pretty much every cylinder wall, the sleeves on the aluminum block go down alot further then cast walls of an iron block. 3.905 is the "standard" LS1 over-bore size. Remember you cant just buy pistons and slap on your stock rods unless you buy the heavy ass Diamond pistons with a .945 wrist pin diameter most aftermarket is SBC size of .927