Did this for the first time lately, thought i'd post how its done, from my lack of experience point-of-view
Since i bought my GT, the rear bumper was always about a 1/2 inch gap away from the taillights - not bad, just irritating - moldings didnt quite line up etc.
Pop rectangular plastic covers off - the ones right above the rear tail lights.
Unscrew the screws underneath, pull em out.
Taillights should pull out now.
Press tabs on bulb thingies, and twist to unlock. remove.
Put taillight carefully aside where you wont trip on it
Under the taillights are some plastic rivet things, that are like larger versions of the ones that hold on the wheel well liner. You'll need to pull the center out (they can be sticky, so be careful not to tear the head off) and then the rivet can be removed.
There are the same rivets on the bottom side of the bumper, take those off too.
Next, undo the screws on the rear side edges of the wheel well liner.
The bumper should now come off with a tug or two.
There is a metal "shelf" bolted on which the rivets were fastened through. I wanted to raise the bumper, so i undid the bolts, and the shelf could be moved up about a 1/4 - 1/2 inch. (May have been put on wrong after a paint job)
Put everything back together, hopefully the fit wont be too tight now! Your done! 
------------------
Black '87 GT Auto - Daily Driver & Autocrosser
Eibach springs, Koni shocks, Kosei K1s, Kumho Ecsta V700s, poly bushings, rear swaybar, MSD ignition, shift-kit, custom intake scoop
