I'd look for 40s, 50s and 60s, maybe up through the mid seventies. About this point they started putting in 10-speed Roadrangers. The RTO-610s, and on up to huge weren't overdrive AFAIK. 13-speeds were but I don't know if Fuller made small ones for the gassers. The ones I drove were 7513 behind like a 335 HP Cummins and the later 12513s were for big power 400s and up. I would think a few hundred dollars would do. Be sure to get the mounts to the frame and the shift-linkage rods and the shift lever and mechanism and the mounts for it.
