I just finished up a T-56 swap into a 92 Camaro and I built my own crossmember instead of buying one. Before I pulled the T-5 I measured from the floor to the center of the output shaft, then did the same on the T-56. I paid attention to get this as close to the original measurement as I could.

Now, at about 65-68 mph I get a decent vibration coming in that picks up quickly by 70 mph, but stays constant to about 100, where it smooths out again (tested on jackstands). I got an angle finder and did the crank pulley/pinion yoke method to check the angle and I'm getting about -3*. I've got a stock torque arm so the only way for me to change the angle is to adjust the mounting height of the transmission. Could that angle be causing the vibration?

I'm running brand new Motive 4.11's, stock steel driveshaft dynamically balanced by Houston Driveshaft last week, T-56 and Spec Stage 3. I tested with the wheels on, and with the wheels/rotors off the car, no difference.

 

ttt