Why plane your intakes w/ milled heads???

Always cut the intake . Never the heads and there is several reasons. But to each his own. I would never cut the intake side of the head unless i was skimming it for straightness. never cut the heads for intake fitment. Thats just me And I ran into problems doing this that trashed the heads. Just think about what you are making thinner. You can't add threads once they are not there. You are also not cutting at a different angle . They have to be cut at a specific angle so it seals on the valley side. so The head would need to have more off at the top then the bottom. Usually double.