I am no expert but you can get gear sets on ebay as well as the other parts you will need. You might think about putting in new bearings while you are at it and what the heck get new clutch plates for the trac-lock.
I also picked up a dvd of how to rebuild your rear end. check out www.technicalvideos.com (differential rebuilding) If you have a dial indicator, the dvd walks you right through the 9 inch.

Hope that helps.