Whats your goal by decking the head? If you just need a fresh surface they will remove a few thousandths and it wont really effect things. If you are trying to raise compression you need to measure the combustion chambers before decking, then you can then roughly calculate how much to remove based on the compression increase you would like.
A KZ1000 head that has been decked 1mm will only have about a 3.8CC difference from stock, you need a piece of plexiglass held on with grease and a graduated cylinder to measure accurately. The surface tension of the fluid will make it impossible to check correctly without it
That's OK. I found out what I needed to know. I'm going to modify the chambers like I was talking about. I'm more concerned about the voids filling with carbon then glowing causing detonation. If I lose a little compression so be it. Who knows, the engine may breath better.