Common Chevrolet engine building takes an engine block and punches it out 0.030” but on our Cleveland cast iron blocks core shift makes this an unwise automatic approach.
My recent build was fine with just 10 over and that gave me 404ci.
20 over = 406ci
30 over = 408ci
The less removed the more stout the block remains and should any mechanical issue damage a cylinder bore I will know there is still sufficient material to clean up a damaged bore rather than look for a new block
Larry