Neither transmission is suitable for the use you're looking at. A better choice would be the SM420 or SM465 4 speeds, which are rated for the use intended.
For the rearend, without knowing what rear you pan to use (Corp. 14 bolt? Dana 70? Eaton HO72?) and what tire size your'e going to run, it's somwhat difficult to pin an exact ratio. For use as a push truck, you won't want a taller gear, but rather a short gear for more grunt. I would say no higher than a 4.10, preferaby a 4.56 ot 5.13 (both stock gearing in the HO72).
