i don't know what kind of engine you have, but i have some smallblock mopar engine-building books. For those it suggests the max. amount you would plane off the head would be 0.060" and for every 0.010" taken off the head, the intake should have 0.0095" removed. Probably not the same for all engines but maybe you can use this as a guide.
"Well done is better than well said." - Benjamin Franklin (1706-1790)