Just got this 76' with a 8"lift, I've got a vibration the u joints just got replaced. There is a short drive line then some kind of support then a longer drive line. The support is real lose around the drive line. This is my first classic and I think it is this support causing the problem "help"

 

The first think I would do is check all ujoints at the shafts that angle the most. 8 inch lift will wreak havoc on ujoints and cause vibrations. If the center carrier bearing is loose it could be causing some vibration. It will depend on when the vibrations happen the worst.