Flanker....ballpark figure is on big block heads, you have to flat mill about .005/.006 per cc. I have a set of 291 rect. ports on my 505 now that have been milled .042. No fitment problems with the intake, but any more, and I would have trouble. You can always have them take an equivalent amount off the intake side of the heads also. Your machinist will tell you what is best. I used the .005/cc figure when I brought my heads to the machinist, and it was just about dead on. Remember also, milling the heads that much will also reduce your piston/valve clearance, but not as much as your cam choice. But it's something to think about. As Pat said, it's the block deck hgt. that's killing you now. But I also agree that pulling it all apart to do that is a pain at this time. If you do that in the future, then you can not only have it decked, but get rid of those stock pistons and get something that can build some compression with a larget chamber head. The small chambers are good, the 215's are great heads, but they're getting harder to find. The large chambers, like the 781's, much more common, but you need a dome piston to make them work well. I'll do some figuring and see how much that milling will help. I dont think it will be too much of a difference though. John