Why not just get a late model Eaton 15k/17k rear axle? Plenty of gear ratio options and you can use standard 10 lug bolt pattern wheels, and it'll still be a real truck. Not a wimpy 1 ton
Edit: it took me several days/weeks of searching for part numbers, cross reference superceded part numbers etc to find all the brake/rebuild parts for my 67 c50. It's hard but it can be done!
I'll be swapping a ZF6 overdrive transmission this winter after I move in my new house. Keep an eye out for that thread