I consider countersinking the intake valves at least flush with the gasket surface of the head to be an absolute necessity, regardless of how much material is removed while milling the head. Back when there were plenty of stovebolt heads in the salvage yards, we would consider any head that needed more than about .020" milled off to make the gasket surface flat to be a boat anchor- - - - -just go buy a better used head to rebuild. As the supply of heads without cracks dries up, it's probably a good idea to do a little more machining to get things right the first time!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!