one thing to note: the carrier shims had to be rearranged in order to get the ring and pinion to mate correctly. on one side, there was a thick and thin shim, and on the other was only a thin (actually three different sizes). the left side had to be switched with the right side in order for them to mesh and be able to get the bearing caps on.
this is my first differential rebuild/teardown, so i dont know exactly how much play is acceptable, but after swapping the gears, the amount of play seemed very small, perfectly acceptable to me. i painted the gear to check mating surface contact, and there was a good amount of smear. i guess the real test will be when it is sent down the quarter mile.
the only snafoo (sp?) was that the bolts that hold the ring gear. on the 3.9 ring gear, it uses 10mm bolts, where the bolt holes that are in the LSD carrier and the 4.375 ring are 12mm. i used a bushing (12mm OD and 10mm ID) to take up the slack between the bolt and the hole. is there anything wrong with me doing this? so bad news for someone wanting to swap 4.375 gears into thier R200 open diff, cuz it wont fit. possibly because those gears came from a newer car, and used beefier hardware.