Get yourself an SM465. It is a GM(Muncie) transmission but I think it will fit your application perfect.
- Bulletproof(came in 1/2, 3/4 and 1 ton applications)
- Cast Iron case
- 12" case length so it is fairly short
- 6.54:1 first gear(great for crawling)
- Easy to rebuild
- There are loads of them out there
- super cheap (less than $200)
I had one in my Jeep for years behind a Chevy 355 running 38" swampers and loved it. The only down side is 1st gear is not synchronized so you have to come to a complete stop to put it in first but if your going to drive it in town 2nd gear is plenty low enough to start from a stop.
Some more information about it.