I have heard that the 89/90 tcases are a little different on the inside than the later ones. I have not verified this info personally though.
You can use a 91-95 tcase in yours. In 96 they changed the rear output shaft spline to a coarse 16 spline (compared to the finer 26 spline). If you have no other options, you can use a 96 and later tcase and either swap the rear output shaft out, or use the later slip yoke that fits the later output shaft (all the trackick driveshafts used the same ujoints, so you can just swap the slip yoke portion of a later driveshaft to your driveshaft).