I gave up the search for a 3 speed OD and decided to go with a New Process MY6 (A-883) 4 speed OD trans out of an '83 chevy 1/2 ton. I haven't installed it yet since I'm going to drop the 327 i'm working on in at the same time. But from what i've read, they're a solid OD transmission and a direct bolt in swap if you get one out of a Chevy. You might need to change rear driveshaft length...I haven't gotten that far along yet. and I plan on fabricating a cross member for it to sit on.
Heres some more info on them if you're interested:
http://www.customclassictrucks.com/t..._transmission/
http://www.classicjunkyard.com/new_process_a833.htm