Heads, how much gain?

do your home work and find which ones flow the best from where the valve starts to open up to total lift of your cam. when you make your choice take them, pour some mineral spirits down each port, see if any leaks out into the chamber. if not you are good to good. if one or a few leaks a little get yourself some lapping compound and a hand lapping tool and lap them in. if you can't get it to stop leaking take the head or heads to a shop have them do it on a machine like the others have suggested. oh, and get an aluminum intake while you're at it. that should remove about 100lbs off the nose.