correction. TJ's did not come with rear disc until 03. i'm not sure if the drum backing plates are the same, but i just did a discbrake conversion on my 97 D44, and just bought the parts for an 03-06 TJ rubicon with rear disc. everything bolted up very nicely. no drilling or modifying required. i don't think there is any actuall bolt up difference between the 89 D44 or the newer ones. the install went so easy, and the difference is so nice i'm going to do it on both my other jeeps.
just went to the dealer (helps if you have connections), told them i needed everything for an 05 rubicon w/rear disc brakes including the lines. total was around $500.