A few years ago I bought, drove a lot, and later sold a 61 F350 with a 6V53T and Roadranger RTO-610 transmisison, 0.80 OD ratio. It was a very nice combination, about 400-500 RPM drops in all gears when shifting from about 2,300-2,400 RPM. It made some serious torque after 1,800 RPM so was very comfortable to drive in and out of 9th and 10th gear, not a large step. Most I hauled with it was between 20,000 and 30,000 lb total truck and all for a couple thousand miles, OD was less used then, but available on the moderate down hills.
https://picasaweb.google.com/lh/photo/zqtbm_-eztH-KxNHD8O4rdMTjNZETYmyPJy0liipFm0?feat=directlink
