Bill,
There was a heavy-duty 3-speed 1/2 ton (torque-tube) transmission in 1954 but not in 1950. The '54 H-D 3-speed was available with different tailshafts for use on all 3000 series 1954 trucks (1/2, 3/4, and 1-ton).
On the 1/2 ton it was the same length as the regular 1/2 ton 3-speed. The column-to-transmission shift-linkages were slightly different. The two transmissions are easy to tell apart - the regular transmission's tailshaft is long and narrow and tapered; the H-D tailshaft does not have the long narrow taper.
My guess is that H-D 3-speed was not common on the 1/2 ton and might have more popular (but still uncommon) on the larger trucks that came standard with a 4-speed (". . . the convenience of a steering column gearshift on 1 ton models for those drivers who do not require the reduction offered by the standard 4-speed transmission").
A heavy-duty 3-speed transmission was available in 1950 on the Sedan Delivery (1508).
I doubt very much that the extra torque (+15%) of the 261 engine is enough to worry about with the standard 3-speed, unless you plan to drag race. I drove for years with no problems using a 261 and the standard 3-speed in a '54 Suburban.
Tim
