I used Britpart (UK Land Rover parts source) greasable U/J's on our D2 front and rear shafts, with a new Precision 617 centering bearing.
So far that has done about 60k miles and with no problems, and we do tow a lot.
Balancing doesn't seem to be necessary as long as the two halves of the shaft are assembled the same way after the rebuild, and the grease nipples (can I use the N-word?
) are positioned on opposite sides at 180 degrees to each other so they balance out on the cardan joint. The single front joint shouldn't have a grease nipple in it for running as it has no balancing weight opposite. A short nipple can be used if your grease gun nozzle will go in netween the yokes.
Mine have plugs in the grease nipple holes as I need longer than standard nipples to get the grease gun onto them. I shoot some grease in and put the plugs back in afterwards. Takes 10 minutes, gets down before long towing trips or every 5000 miles.
Our original shaft did 130k miles before it was changed.
Peter