Do not machine the springs seat down by that much. I can't figure out why you need all that installed height. I'm running .620 lift and my installed height is 1.720 and I know Crane and a couple others make springs that will take that much lift with a 1.7ish installed height.
Whatever you do, go to b3racingengines.com and read ALL the tech pages he has posted. I can absolutely promise you that you will need to correct your geometry.
Make sure your valve job has a top cut .060 wide and .100 would be better but sometimes it's hard to get, especially if the valves are bigger than 2.02 so here is a case where bigge isn't always bigger but you already bought your parts so you are married to them.