i say find a new tail shaft guy
but then again your rear end has been lowered as well hasnt it ange, maybe the problem is at the diff end with the angle not at the gear box. if you have to move the gbox up to reduce the vibration would moving the diff down (raising the rear end slightly) do the same?
Maybe experiment with some lowering blocks but use the to raise the rear end to see if it alieviates the problem. at least you wont have to fabricate any thing .... YET.