Why not just go disc front / drum rear?
Unless you are autocrossing/Pro Soloing this car, the difference between drums vs. disc in the rear is hardly noticeable. The front disc do about 80 percent or more of all the braking based on the brake bias.
If you wish to pursue the rear disc conversion, check out the
www.moparts.org message boards, go there and look for Doctor Diff. He has complete conversion packages available, including rear disc conversions (I believe these may be Ford Explorer rear discs adapted to the 8 3/4 rear).
Check out this thread for Doctor Diff info.
http://board.moparts.org/ubbthreads...96&Words=+cnxt&topic=&Search=true#Post4978372