decking a 360 block

I have read about guys taking so much off the doll pins bottomed out keeping head gaskets from sealing. Not knowing what you are trying to get, or where you are now needs to be stated. Some other things you need to look at are how high do the current pistons come out of the hole (if at all), how much do the valves go into the hole (cam lift), how thick is the current head gasket. Most machine shops will cut just enough to true a block up not to gain compression.