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.
06 GT- CDC shaker w/ JLT, Dynatech LT's/catted xpipe, M80 racepro mid mufflers, UDP's, Hurst STS, 4.10's, XCal II(tuned by ProDyno) 326.8hp/331.2tq
89 LX- 306, 9.5:1 SRP's, Eddy RPM II/heads/75mm TB, Lunati cam 221*/232* @ .050" and .557/.554, Comp 1.7rr's, 24lb inj. 200amp alt., 12" elec. fans, BBK CAI/shortys/hpipe, Flowmaster catback, MSD 6AL/coil/Distributor/wires, BMR UCA/LCA's, Built AOD w/ TCI 3000 stall, almn. DS, 3.73's, 31spline mosers, Auburn Pro diff. battery in trunk.