My 1966 dart race car.

I had a vibration also! I did not go to the extent you have! [great effort!] However, my problem was in the drive shaft. I used a dial indicator and checked the shaft just out of the transmission and again just prior to the companion flange. The run-out was substantial! So I took it back to the "place of birth" and had them check the shaft on their lathe, they also saw the run-out. Come to find out, I use the A & A slip yolk which has the removable caps. When I replace my transmission after a rebuild, I did not mark/index the shaft to the slip yolk [my fault] I had the Driveshaft shop install the assembly with the "least" amount of run-out and rebalance the shaft. The problem is gone! Like you, I could not get my car down the track! If I raced it [I made one full pass] I was sure the drive shaft would wind up in my lap! I have many laps on this driveshaft and two different 999 combinations, and no vibrations...now that I have painted [indexed everything for assembly stupidity!] Good luck with your Vibrations!