I had (have) one of the 85 anniversery models w/302. "special" blue paint w/white wide body molding. The same color that was standard of every 86 I saw (seemed that way!). I changed to true duals all the way back---had to wing it though and was really simple. with some minor mods.
Mustang unequal shorties (fox body of course), Mac "off-road" H-pipe, mustang tailpipes------all 2 1/2".
1. flow tube extentions to acct for extra wheelbase.
2. fuel filter had to be moved, was in way of pass muffler.
3. tailpipes kinda close to front corners of fuel tank.
4. used "LX" tailpipes (w/o turndowns) use turn-down extentions for extra length to rear bumper.
5. Double-hump x-member---std fox body.
6. hanger bkts on frame not there for rear muffler mts. available from fomoco.
7. rear tailpipe hanger bkts have to be fabed.
You may have to screw around with plastic fuel lines or replace. Re-locate of fuel filter causes some fabrication. Fox T-bird is only long wheelbace mustang w/facelift!! Dont know about 87-88's. Suspect they are not greatly different from 83-86 except for 8.8 and disc brakes (TC)