So, at work today, I am a snowboard instructor, I looked at an old Tucker sno-cat that they had. Looking at the axles it looked like it had some sort of Dana 60 or 70 or something like that with a pinion snubber. So I search google for some info on them and they could be had with industrial 318's or 360's mated to Allison Auto 4-speeds, or NPG 5-speed manual tran's. I have no clue about the ratios but they could be a viable option for tran's and its pretty cool that they used LA engines. Also the diffs could be useful since they have snubbers.
I kept looking about them and some of the newer ones use 727 trans mated to cummins 130hp diesels.