Yes, Onkel Udo (Deutsch sprachig offensichtlich), I've retained the original shafts and they had been scribed and paint-marked for alignment at the factory.

A driveline shop recently helped me replace the Flex Plate, Carrier Bearing and Mount, and both U-Joints. They took care to mark the flange for alignment. Orignial flange bolts were reused. They do not have a jig to accomodate the Flex Plate.

The vibration is similar to what you describe, except it seems fairly constant. It causes a mild buzzing, tickling sensation at the pedals, shifter, steering wheel. A person driving the car for the first time would probably not notice, but having driven it for over 20 years I notice the change. There is a chance the vibration is originating from something else (motor), and I'm feeling it now that the driveline is stiffer and not absorbing the movement. I also replaced the soft transmission mount recently, creating a stiffer system.

I've been told the factory U-Joints are "crimped" or "staked" in place, and replacing them with clip locks might create enough imbalance for vibration.

I have called a few other shops with no success. I will try 4x4 shops. At this point it's looking like I might need to send out of state for balancing.

UOII is correct about having the u-joints in phase--and with regular driveshafts using 3 u-joints that leaves only one of two positions that could be in "factory balance" (assuming both halves from original). With the flex disc at the front that method doesn't apply so if the two halves are original and the orientation wasn't marked, "visual" alignment may involve a number of visually correct but not "in balance" solutions. I don't have much experience with the flex disc system so never had to take into account how the disc sits when the rear half u-joints are rotated so the "crosses" are parallel and vertical to the ground. It does seem like the original poster does need to find a shop to balance the works. As suggested a 4x4 shop--or a truck driveline specialty shop should be able to do the job. -- Dave