A torque tube rear end only has one universal joint, the one behind the transmission. The mounts where the rear axle tubes bolt to the springs have pivots built in, sort of like door hinges, to allow the rear end housing to move in relation to the springs as the vehicle negotiates bumps or the load on the chassis changes. When the driveline is changed to an open driveshaft type with a u-joint on both ends, the spring mount hinges have to be welded solid to keep the housing from flopping around anywhere it chooses to go as torque is applied to the rear axle. It's necessary to establish the right angle between the pinion flange and the driveshaft before doing the welding. I don't know if the early-style center housing would change out with the enclosed driveline, but if it did, you'd probably have a gear ratio that would pull stumps, and very low highway speeds.
Jerry
