Here is another link exclusively for the LX that gives a year by year of what was changed and such. The GT's are touched on briefly when the subject of the changes to the 5.0 cars are mentioned. I hope you find it useful.
If it were me, i'd find one with a good body first and foremost. Preferably a 5.0 so you already have the 8.8 rear, computer, etc. but a 4cyl car will work. I wouldn't worry about forged internals. The cars have probably racked up plenty of miles by now so, once again if it were me and i were building a street car that would see occaisional track time.....i'd build a new motor any way and put a forged bottom end in it. There were slight changes in the interior after 89 (steering wheel w/ air bag, AC *****, dome light, etc.) Good luck, i hope you find a nice one.