The 1955-62 1/2 ton center section will fit in place of the torque tube diff from 1940-54 on 1/2 ton pick-ups. Same axle splines.
The 1955-62 standard ratio is 3.9, although 4.11, 3.7, and 3.38 were an option.
I have done this so many times with T5 swaps and it works great. This way you do not need to worry about mismatched brakes or modifying e'brake cables.
