Bigger trucks (over 3/4 ton) had a supported carrier bearing. Needed for the longer bed and longer drive shaft. The torque tube needed some support and on the short bed trucks that was the cross member behind the trans mission. With out it some whip forces would only have the rubber in the rear axle to spring mount for control. The bigger trucks had the carrier bearing and a 2 piece drive shaft. and a cross member to suport it. You do have to be able to remove the support and cross member if you want to service the torque tube. The E brake set up (drum on the drive shaft) was also supported. The SM420 transmission will have either the torque tube bell end or the flat end with a seal depending on the driveshaft used. Those will interchange by the way.Older torque tube to a newer transmission? no problem. Just swap the bell end for the flat one and you are good to go. Older transmission to newer drive shaft? Again, no problem. Just swap the plate for the bell and you are good too. The output yoke matches the bell(torque tube) or it matches the the open drive shaft. I keep them together for each application. Does the length of the drive shaft matter? Probably. But the drive shaft in the Emissions cheating "heavy Half ton is a long one with no carrier bearing. Late 70s maybe. Keep the mount and the cross member. The Engineer had this discussion with the Accountant already. The Engineer won.
