Which transfer case depends on what you want for 4WD. The NP231 is the standard tcase, but the full time version is the NP242. So, outside of that there are a couple of things to look for. One is the spline count on the output shaft of the tranny. They came in 21 and 23 spline. The later AX15s had the 23, not sure what year that started. The other thing is the vacuum switch for the front end. The early D30s had an axle disconnect that is operated by the vacuum switch on the back of the tcase and had mechanical speedo cable. The 96 and up for sure had electronic speedo and speed sensor for the OBDII. Same cases, just different inputs and switch and speedometer stuff. It can all be changed however. But the best thing to do is find another 87 - 95 donor rig and get the tranny, tcase, front and rear driveline, tcase linkage and front end. Steering and suspension are the same.