The T-5 tranny is a really good option, but it's not really a "bolt-in" deal. I was planning to go this route on my '68 (3.73 rear), but I'm now looking for a New Process A833. It's a 4 speed (3+OD), has a .73 OD, and is a direct replacement for my tranny.
Go here: http://www.inliners.org/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=000453
There are two other links I posted on there too. The T-5s didn't only come in S-10's either. Look in Astro Vans, Caamaros, Firebirds, and a few other I can't remember. The one I've got came out of a Camaro. It's a World Class, has a .63 OD, and my current speedo gear will even slide in place of the electronic one on the T-5.
Email me at
[email protected] if you need links or any info. I don't drop by here much. Good luck. John