Is the torque tube the same length for the 3 and 4 speed options in the 1/2 ton?
Yes - and, of course, they both use the same u-joint coupling assembly housing-cover.
The rear "housing" of the enclosed drive-shaft SM-420 4-speed [1/2 ton only in 1954] is the bolt-on cast-iron end-piece for a torque-tube.
The 3sp and 4sp u-joints yokes are different.
If you have pre-1954, you should use a rear-of-transmission mount on the existing frame cross-member.
A reproduction mount is sold by Classic Parts.
https://www.classicparts.com/1947-54-Rear-Transmission-Mount/productinfo/79-204/
