The front leading edge of the fender where it mounts to the buper cover is the same.If you look at the opposite side where the filler panel would mount it the opening gradually gets narrower I would say by about 1 inch the closer you get to the bottom of the fender opening.The early fender is a little more squared off in that area where as the later fender looks like the corner is cut off if any of this makes sense.It is the area where that little panel mounts that is different in size.the rest of the opening is the same.they changed that area so when you turn the wheels lock to lock it doesnt rub that panel with the larger 16" wheel.If you have ever put ponies on the 87-90 cars and they rub that is what ford designed for.

Mark