Carrier Bearing ?

[Accelo]

My 1970 6-cylinder three speed truck had a two-piece drive line from the factory. I thought this was interesting as it a SWB truck.
Typically, when the drivelines get longer, engineering will add the carrier bearing and/or increase driveline diameter.
The larger diameter is to combat driveline whip. As an example, the front drive line is short and and only requires a small in diameter for this reason. The longer they get the bigger around drivelines get. This is required to combat whip. The longer the length and the higher the speed the more tendency to whip. It makes sense that newer vehicles with Overdrive transmission tend to have more whip issues. Just look at the diameter of some of the newer truck’s drivelines, they are huge. Drivelines also have critical speeds. You want to stay below the critical speeds of the driveline or bad things happen quickly. Extremely low differential ratios combined with high rpm motors and a overdrive transmission can be problematic.
BTW I don’t consider a joint change as a low-tech easy job. Too many people use hammers instead of a press. They tend to dent the tube when inserting it into a vise to beat the joint out. If the removal force is in the wrong spot the mechanic will typically bend the yolk ears getting the driveline apart. I can tell you most the drive-lines I work on have been abused by a mechanic in the past.
Cheers.