[HO455]

Actually the OP is correct. My 67 had the exact same set up in it. (See the less than optimal photo) As far as I can tell the base 1/2 ton trucks came this way. The rubber mounting of the carrier bearing absorbed the back and forth motion of the drive line as the axle travels up and down. The only sliding joint in this set up is the yoke at the transmission.

The OP is on the right track with his idea to move the carrier bearing. When the truck left the factory the bearing was in a neutral position in the bearing mount with the rubber centered with the truck at ride height.

When the axle travels up and down the rubber flexes forward or aft though it's designed range of movement.
When the truck is lowered (Or raised ) this forces the bearing's rubber mount to move beyond its designed range of movement. This results in the rubber tearing off the bearing or the carrier bearing mount starts flexing until it fails.

When installing a carrier bearing the truck must be at ride height (No using the 2 post lift for this job)and the carrier mount must bolt to the crossmember without being pulled or drawn into place by the bolts. That allows the bearing's rubber to be centered or neutral and have sufficient range of movement.

The other issue I've heard of is that the replacement bearings available today don't have the same range of movement that the original GM ones did but I've never seen a side by side comparison of a NOS carrier bearing with a modern repop. It wouldn't surprise me if this were true.

To the OP I would do as your planning and when you've got things bolted up remove the springs and then do a range of motion test. Find some way to verify the carrier mount is not flexing and that the yoke isn't bottoming out.

When I needed to replace mine I converted to a billet bearing with a sliding joint in the rear shaft. The reason being that my Burban was on air bags and there is no way to find a reasonable neutral position for the factory carrier with the larger range of motion that a changing ride height that being bagged causes.

Good luck and let us know how it works out.