For a stock rebuild, take off only what is required to true the head and clean up the gasket surface. 5-10 thousandths is usually plenty. The head shop will do that automatically, unless you aske to take more. Taking more than required is a "hot rod" technique to raise compression for performance. You can measure to the intake inlet to determine how much has been removed previously...Id o not remember the numbers, but someone will, or you can search the threads as it has come up many times.