Centering a Rear....(Axle)

[72longbed]

Well I tried to move this over from the Drivetrain Board but don't know how so here goes:

My 72 C-20 has a 1974 14 Bolt Full Floater under it. Coil springs and trailing arms. I'm getting alot of drivetrain vibration. I noticed that the way somebody welded the trailing arm perches on the axle tube it puts the center of the pinion housing off to one side about 1 1/4", (when measuring at the same point on each trailing arm to the center of the pinion housing). I have an adjustable panhard bar and the rear is now centered under the truck in relation to the wheel well openings.

Questions: Do I only need to be concerned with where the center of the pinion gear, or rearmost U-joint, is in relation to the frame of the truck at that point? Is it OK to move the center carrier of the two piece driveshaft left or right to compensate for the rear? Is this a common problem? Can it be causing driveline vibration?

Thanks for any helpful info,
72longbed