This calculator will calculate the amount that needs to be milled on the intake face side of a V8 head.
Some engines have a different angle for the intake side of the head.
(intake side is not 90º to the head deck side)
So it is not a straight one to one ratio.
Some of the popular American heads are listed.
The intake flange itself could be milled, but one would have to realize the intake would be useable for just that head.
The Bottom of Intake data is for certain engines that have what some call 'China Wall'.
The block ends and/or the intake bottom need milled also to allow it to be lowered.