Call Claude at Drive Train Specialists, 1-800-521-0628. I just ordered a set of 4.56 gears, install kits, and a Detroit Tractech posi unit for the rear. Truetrac is what comes from the factory.
I saw some recomendations for them on another thread, and he was knowledgable and helpful. He might even knock off some off the advertised price on the web site. The prices were comparable and/or better than Summit Racing and Jegs.
http://www.drivetrainspecialists.com/index.html