So the newly balanced shaft with all new bearings and guibo in front (rear one appeared to be close to new so didn't replace) Eliminated the vibration under normal accelleration.
But if I floor it then I still get a pretty wicked drivline vibration. It still feels like it's coming from the rear.
I suppose I could replace the rear guibo as it's the only thing left which isn't brand new but it seems perfect.
Could tightening the 2 large gland nuts with the car off the ground really do this? I must be missing something.

or.... could the torque converter cause this?

__________________
190D SOLD
2.5 non turbo
5 speed manual transmission
Build date: December 1985
W211 E320 CDI
W126 350SDL
X204 GLK 250 Sans Bluetec

Recall that the center section (aka diff) is mounted in rubber. As torque increases, the upward deflection of the pinion nose increases. At a greater angle between the driveline axis and the pinion axis, there will be greater vibration.

I didnt consider the diff mount, though it is now only under full throttle so perhaps thats enough torque to oscillate the diff

__________________
190D SOLD
2.5 non turbo
5 speed manual transmission
Build date: December 1985
W211 E320 CDI
W126 350SDL
X204 GLK 250 Sans Bluetec