I have a set of 00' Gt seats that are bolted into my 81' Fairmont. The Fairmont is a Fox body car and the seats were a direct bolt in item, no mods required. The floor pan use in Fox body cars was the same from 1979 thru 2004. I do not think fitment will be an issue. If the seatback is higher, then yes the headrest will be closer to the roof, but i do not think that is the case.
I've had 03 GT seats in my convertible for several years. They bolt directly in, but take a little bit of wiring work to get the power functions working. They do sit noticeably higher, but it isn't an issue for me. The exponential increase in seating comfort is more than worth the trade off in seating height.