If you have a motor that has been bored .030 then milling the block .060 only bring the cylinder volume back to very close to equal. So unless the piston shape is changed, and the head and gasket are the same, the compression would stay very very close to the same as original when the block is milled .060 after being bored .030.In the case of dish pistons the depth of the dish will be less so there will be some increase but very minimal. Paul
