there is a brace that holds the fog lights plus the bumper cover of course, not sure if anything else is needed. Someone may know about wiring from the switch on the dash to the fog lights themselves.
Pretty sure the wiring is all there on all models. Just add the fog lights and switch to work. And of course the associated parts as karthied mentioned. The problem is the trim. To look right you'd need to put all the GT side trim all around (or cobra). It's a pretty major hassle unless you want the full GT look. If you just want some driving lights you can mount them how you'd want and get the switch and run the wiring from the fog light harnesses (Present on LX's at least 5.0's) to the lights you choose.
Wiring is present on all models. Just need the actual switch, and fog lights.
You'll need to add the lower fog light bracket, and then install the bumper cover. You also need to add the front fender GFX extensions forward of the front wheels.
Then the main issue is mismatch, as the GT body trim all around the car is different than that of an LX. So looking from the side, you'd see the different trims. Also, a GT bumper on an LX without the rest of the GFX looks like a beard.
Beard? I can vison that, I was thinking more like an under bite, maybe look at some of the aftermarket stuff? I like the gt look but unless you got a complete car to r&r maybe. I've got some side skirts and a set front fender pieces from a wreck but the car got away before I took the metal side strips
I likely have at least one part of every year from 79 thru 93 someplace in that garage.