[The_Jed]

I totally understand, $60 goes a long way for Fox parts!

The ring and pinion from an Exploder or F150 would fit, but not the whole rear end, they use leaf springs.
To have a bolt-in housing swap you'd have to snag one from another Mustang, an '83-'88 T-Bird or Cougar or an '84-'92 Mark VII.
The bare housings width is the same on Mustangs from '86-'98 but the '94-'98 track width is about 1.5" wider due to the ABS ring inboard of the axle flange, as is the Mark VII housing.
The '99-'04 housing is about 1.5" wider than the '86-'98 so the track width is an additional 1.5" wider or 3" total wider than an '86-'93 Fox.
Any of those rear ends would physically bolt right in but would require some re-routing of the brake lines.
The '94-'98 rear end may cause some rubbing of the outer edge of the rear tire on the rear wheel opening and the '99-'04 will most likely cause rubbing.

You could snag a 7.5" rear from a V6 equipped SN95 and kill two birds with one stone; 3.27 or 3.55 gears (I think) and 5 x 4.5" bolt pattern. The newer 7.5's are much stronger than they were back in the '80's.
I had planned to grab the k-member, A-arms and spindles from a '94-'98 V6 to swap into a Fox, cutting and re-welding the motor mount pads for a 1" rearward relocation.

If you use the '99-'04 spindles you'll NEED offset rack bushings since Ford raised the point where the outer tie rod bolts to the spindle, on the spindle it's self. If you don't use them you'll encounter tons of bumpsteer.

SN95 A-arms are 1" longer than those on a Fox so you'll gain about 2" of track width up front as well. You'll also have tons of negative camber, if you don't slap on a set of caster/camber plates to dial some of it out.