Check out Paul Cangialosi. The page is 5speeds.com. He's definitely an expert on the T5 and Muncie transmissions. I'm ordering a Muncie from there for my '64 Impala sometime this summer. He has a bunch of YouTube videos that walk you through every part of the project plus a few books he's written.
Muncie Super T10 T5 T5 World Class and all Manual Transmission rebuild kits
www.5speeds.com
EDIT: well, crap. Looks like the T5 rebuild kit is out of stock at the moment, I'd call them and inquire about the turn around time. Personally, I wouldn't deal with anyone else when it comes to transmissions.