I would rethink the motor mounts. If the center has fallen through they transmit a tremendous amount of noise/vibration as the metal of the mount beats on the frame.
I have seen about every balancer problem imaginable including wrong oiut of balance balancers and can't imagine one causing the problem you describe.
Does the engine seem to be running properly other than the vibration? Is the power OK? A diesel with a big timing problem will shake terribly and not be related to single cylinders.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician