According to my parts book, there were 3 different depending on year. One is listed for 1947 only, which was the last year for the old style tranny. One listed for 48-50, same part for either 3 or 4 speed. And one listed for 51-up. I believe the only difference between the 48-50 unit and the 51 and later was a change in the torque tube bushings, but I'm not 100%.
If your's is a 48-54, you would be able to swap a 48-54 1/2 ton 4 speed for a 3 speed,or vice-versa. The tranny must be from a 1/2 ton and you must use the corresponding u-joint for the tranny.
Bob
