It doesn't make a lot of since the way its worded does it. If you could just change out the center section, you wouldn't have to weld up the perch pads. If you have to weld the perch pads to the axle house, then you could use any axle you wanted as long as it was the correct width and you wouldn't need a 50's style axle.
I think you will find the 3/4 ton would have a even lower gear or same has what you have, in which case you wouldn't gain much other then a open drive line.
The correct pinion angle is set by locating the pinion angle in relation to the transmission tail shaft angle so the u-joints will work as they should. Since the crankshaft/transmission angle is set, the only variable is the pinion angle. The torque tube has only one u-joint so the pinion angle doesn't come in play as it does with two u-joints. In order for a u-joint to function and last its intended life time, the roller bearings in each cap must turn, and to do that the u-joint angle should be at least 2 and no more then 5 degrees. If the drive line was set with no angle between the output shaft and the input shaft, you could get some strange vibrations and a very short life from the joints.
Hopefully someone with some 40's truck knowledge will come and explain this a little better. Maybe we are missing some information.
Joe
