http://en.wikipedia.org/wiki/Torque_tube

Others will have to provide information about other conversions; however, the only conversions that I know about (that retain the torque-tube) is to replace a 47-53 4.11 rear-end with a 1954 3.90 rear end; or, replace the 4.11/3.90 rear-end's ring-and-pinion with a 3.55 ring-and-pinion (the 3.90 would also need the earlier ring-gear's carrier).

Tim