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.
Thanks for the response, small block chev. I'm gonna catch some flack, experimenting with 305 heads. I've done them up. They look good. They look like they may breath, for what they are. I used a block that was cracked down towards the lifters. A good friend of mine operates a machine shop, told me I would be alright because the crack was towards the lifters. Water in oil. Don't know for sure where water's coming from. Suspect the block. Never had any problem with the van it came out of. Took my 383 block, redone, used it, gonna try again. Trying to figure out where water's coming from. Thanks again. When it rains, it pours!
The small block Chev is an easy one to figure out how much to remove from the intake manifold face to match your shaved heads. Since the heads intersect the block at 90 degrees and the intake face is also at 90 degrees you would remove exactly half the amount off of each intake face.
For example, if you shave the heads or block 0.010" you would have to remove exactly 0.005" from each intake manifold face to retain the original orientation. This only applies to engines that have 90 degree gasket surfaces.
To do engines with less or more than 90 degree gasket faces use this simple formula,
For a 60 degree V6 with 0.010" shaved from the head: TAN 60 X (0.010" / 4) = 0.0043" from each intake manifold face.
Just remember to check the manifold faces to be sure you have the correct angle, not all engines have 90 degree gasket faces.