You have only 3 choices:
1. forget the rear disc replacement if it looks okay - my '91 has 240k on the original and it's fine.
2. Unbolt the exhaust and the heat shield and the center bearing support.
3. Unbolt the differential and wiggle it back a bit (ugh!).

Since you're doing the front also, I suggest you do method #2 above. Then you can check out the center bearing and u-joint, and it makes the front disc installation easier. The exhaust can come off in one piece if you support it properly as you lower it. Unbolt it just behind the headers, unbolt the support on the tranny, unhook the o2 sensor wire under the passenger floorboard, and pull the rubber doughnuts off the mufflers. Two guys makes it a lot easier.

DG