So far we have changed everything conceivable item in the drive line but have not done the shimming experiment as recommeded by a previous Volvo technical service bulletin ---- before we start the shimming experiment --- is there anyomne out there who has had any succes with the shimming (up/down) of the center stage and/or center support bearing please

Why not do it right ?
If there is play in the tailshaft bushing fix that first. Check u-joints for play.
If it still vibrates, check all mounts and replace as necessary. If that does not help, check the axle for straightness.( very unlikely that it is bent but could happen)
If it still vibrates ,take it out and have u-joints checked and shaft balanced by a driveshaft shop.
In the unlikely event it still vibrates ,driveshaft angles may have to be checked and corrected but since any deviation there is most likely caused by bad mounts it would be taken care of by replacing mounts.

I can attest that the hose clamp method worked for me.

You can go about marking the shaft first or do what I did. Just put it on and drive.

If it sounds bad or worse, rotate 5 degrees and drive again. Repeat until you have your best location.

Sometimes using two with the worm screws slighty offset from each can help in getting better balancing resolution.

Good luck.

I've never had success with the shimming--it has tended, in my case, to merely shift the vibration from one speed to another. I did, however, have success by crudely balancing the driveshaft on the car. Maybe it was just luck, but I started with the assumption that for the shaft to be out of balance it must be deformed in some way. With one rear wheel of the car safely lifted I ran the motor with the car in gear and scribed a mark of the driveshaft in front of the center bearing using an awl or similar--the awl scratched through the paint on one side of the shaft, marking the (presumably) heavier side. I attached a hose clamp with the heavy side opposite this mark and voila, no more shudder. After replacing the center bearing and the engine and transmission mounts a few weeks ago, I removed the hose clamp and the vibration was obvious as soon as I pulled out of the driveway. Who knows.

More common faults lie in the tailshaft bushing (wear makes the driveshaft wobble). But also check the engine and trans mounts--if they're shot the engine/trans can be an inch or so away from where it should be. Volvo did offer a tech bulletin about shimming the center bearing, and I know it suggested to go one way first then the other. Good luck!