. . . It has a different torque tube length and a different "Ball joint" from the 3 speed. . . . Find a 4 speed, and the floor cover, Find a torque tube and the "ball" and you can change it all out. Sell the 3 speed, and torque tube and you might come close to even.
You would not need a different length torque-tube rear end. The 1948-54 truck three speed and 4-speed transmissions are the same length. You will need any year SM420 4-speed with the torque-tube fitting; or, you can put a torque-tube fitting on the end of any year SM-420 transmission.
