The only difference between the '91-'93 fenders and earlier ones is that the later fenders have the fender flare higher up on the fender and there's usually holes drilled in the bottom front part of the fenders for the fiberglass fender extensions that bolt on to the urethane front nose.
Another difference in the later models is that the Engine crossmember is wider so the control arms stick out slightly farther which increases clearance between the tire and the fender/fender wells.
------------------
Mustang Parts Specialties ripped me off, it could happen to you as well.
'84 Mustang 5.0 LX
my LX
'89 Mustang GT
my GT