65 barracuda vibration

Y
Let me get this straight.......you used the original drive shaft for the 7 1/4 rear bolted up to the 8 3/4 with no modifications to it; is this correct?
Yes, it is the stock drive shaft from the 7 1/4. I know it isn't perfect. I'm gonna be pulling the engine and trans and will have a new driveshaft made for the new engine/trans.