Darwin,
As far as the shop manual goes, all 1/2 tons had torque-tube though 1954 model year.
1955 first series (same body as '54) went to open driveshaft.
1954 3/4 & 1 ton with 3-speed tranny had open drive shaft, whereas '53 & prior had that short "torque-tube" back to the carrier bearing, then open drive to the rear end.
If you still have that vibration after you've corrected all your drive-line angles, check the tailshaft bushing in the rear end of the tranny (where the slipjoint & and universal yoke are): I had a similar vibration in my '54 3/4 ton, and it turned out to be a very worn bushing.
Hope you get it licked!
