Drive line vibrations

It is the same drive shaft so I would have to shorten it is about my only option then.

You will have to check the clearance at the front yoke to the trans tail housing with it in the car. Some setups had 1.5" to 2" of clearance up there to begin with. See if you have that rubber cone boot on the rear trans dust seal, or if it is just the flush fit seal without the dust boot. Good to have at least 1" clearance from the actual end of the transmission tail shaft, a little more is ok too. That sliding yoke shaft slips up in there quite a ways.