Hi Steve:
I had my transmission and overdrive rebuilt by Robert Jasper in Ca. Benefits are that he had a test bench set-up to make sure it was all correct, he knew which parts required premium replacements (i.e. synchro rings), he has done a bunch of them so knows what the issues are, and he returned everything in like new condition and it has worked great. Downside is cost (about $900 for rebuild of Tranny and same for overdrive) and I got hammered on shipping from and to Hawaii. But I would not think it wise to tackle the job as a first time thing. Save your mechanical skills, time and motivation to do more straightforward jobs like suspension, etc where you can get involved but not risk messing up on such a critical component that is hard to get to.
Dan