Im sure the fenders will interchange, but I think you cannot fit as wide of a tire in the front with the 87 to 90 fenders, or was it 89. Bumper covers should be the same. I do not have proof of my answer, but Im sure someone else will chime in.
The inner fenders are different also - year specific. The bolts are in different locations I was told by the Ford partsman here. According to the Fox Body Guide, 91 is when they were in-larged.
And to add to that, the 91-93 fenders need different fender extensions. Due to the larger wheel opening, the fender extensions were trimmed accordingly.
And to add to that, the 91-93 fenders need different fender extensions. Due to the larger wheel opening, the fender extensions were trimmed accordingly.
thats probably why when I put my gt ground effects on, the side piece (skirt?) from the front wheel along the bottom of the door doesnt meet up tight with the piece right infront of the rear wheel. Theres about 5/8" gap. The front fender extensions fit nice.