40 years of building cars and god only knows how may GT FG parts I have installed on countless models of Porsches.
your going to have to do something to get them to fit and at least look ok.
on this 944 build for a customer yet more GT panels to deal with. the one piece nose and wide body QTR panels. the hole areas behind the front wheels had to be cut off and made totally new the shape was nothing like the shape of the door . and I mean nothing like !!!
for the rear QTR's I had to cut the areas off where they mount to the factory QTR's and make all that area new. then the bottoms of the rear QTR's I also had to cut them off and make them lower and extend the parts to meet up to the underside of the factory QTR's to mount them.
I still am debating if I'm going to fix the big dimples on both side of the nose ??? they are the same on both sides. when they made the mold they maybe should have filled the dimples in. the other 944 wide body we did was the same way.
the GT RSR flares are not any better for fitment. your going to need to make the parts fit it's just a matter how fussy you are for how they look.