have you checked or searched for this on
www.thirdgen.org ? i'm sure plenty of guys have gone with a FAS efi setup on a setup like yours...or at least had questions and had answers given. In a few years when I plan on building a stout 406 or 427 small black I plan on a setup like FAST/atomic/etc efi Its still years down the road so I haven't done much research yet. check thirdgen, use the search feature, might find some help there.