I bought a pair of mint 1986 GT lenses and housing on ebay a little over a year ago for the price of just one of those lenses from 50resto.
Before I put them on I sized up the housings of the 86GT with the lenses already in them to the LX's on my car. The housings were very very close to each other in size. Only difference was probably about a couple of millimetres in difference.
Yes, the LX lenses are "bulbous" or rounder than the 86GT's or the Cobra's. I knew before I put them on that I'd have some overhang from the hatch lid and yes, I do. It's recessed about half an inch. Unless you're a foxbody stang buff, you'd never know the difference. I don't know how it would look recessed on a notch/trunk though. I think the hatch let's me get away with some of the overhang.
I went down to the local autoparts store and got a roll of black pinstripping material sold in the autobody section and was able to pinstripe both lenses with about a foot left to spare. Again, unless you got up really close to the lenses or ran your fingers over the surface, you'd swear they were true Cobra's. I was rather meticulous as to making sure the space separating each stripe on the lense was proportionate.
As for swapping out the lenses, the ones I got from ebay the butyl seals were dry and the lense of one of them was rather loose. So I gently pryed the lense off the housing using a large flathead screwdriver and just resealed the lense to the housing by covering the old butyl with fresh sylicon sealer. The I just re-seated the lense in the housing and wrapped tape around the lense and the housing to keep it snug for drying and left it overnight. Next morning I reinstalled. Holds great now!!!!
Even though you can do this job with the housings still attached to your car, I highly advise that you take them off and do it right at a workbench or kitchen table. That way, you can clean the housing also.