The Stovebolt Site Forums The Shop Area Engine Shop Overdrive for a SM420 4-speed?

The truckstell unit is one of those things that you may see one in a lifetime but unfortunately someone is using it in their truck. The BW OD incorporated into a torque tube was once a popular conversion, however those have dried up also. It is still possible to find a BW unit and have the machine work done but in my opinion it would be cost prohibitive. You would have additional issues being as your truck only has a partial torque tube. There are 3 speed units available for 55-69 cars & trucks which work fine but to use one you would give up your 4 speed. It would require linkage, driveshaft mods, etc. I think what Larry was referring to is using a BW OD unit from a 66-69 Saganaw 3 speed and attaching it to a passenger car 4 speed. There should be some info on that in this forum. You could also replace the entire rear end with something from a later model truck, however it would require some modifications also.
Finding the correct width & gear ratio would also be a challenge.
You would probably want something with a ratio in the mid 3's to make much of a difference.
Fred