vibration
I'm not sure but with the driveshaft hitting your drive shaft loop before, you might want to check the drive shaft length. It sounds like the drive shaft may be to short and that's why the vibration. I usually put the drive shaft all the in to the tranny and pull it out 3/4in. Then take your measurements. Do this when the car is on the ground. Or you could have a bad tranny bushing. But it sounds like your making great progress Carl.
Just my thoughts