I think fr500's and ford gt heads will both bolt up to a normal 4 valve intake. I was looking and I can get the heads complete brand new from the dealer for $1345 so Ill prob just buy them there.
I can't remember where I saw it, but the Ford GT heads and the 00'R heads both have the intake bolts in a slightly different spot.
Boss330 might know for sure.
My understanding is that the FR500 heads are direct replacement for 99 and up 32V ( except GT) heads.