Bad vibration

So he didnt balance the driveshaft...perhaps an output shaft bushing?
I was also going to mention the pinion offset. It should not be "0" it should be slightly under 0 so when you wrap up the rear, it becomes 0. Nose down a few degrees depending on your setup.

I agree, but I didn't want to get into a greatly detailed explanation when the man should be reviewing his service manual when the problem starts getting complex.