Just a suggestion that I've used as a mechanic hunting vibrations, kick the transmission into neutral when you feel the vibration to see if it changes it at all. Sometimes it's difficult to isolate a vibration from driveline, or engine. Letting the engine drop back to idle will further isolate the source. If it's felt in the steering wheel, it's normally in the front end, if it's felt everywhere it will usually be in the drivetrain.
A bent driveshaft will still vibrate with new joints. I would get the rear wheels off the ground, and observe the driveshaft for runout while turning in gear. Or have it checked by a competent driveshaft shop. It's not that hard to bend an old driveshaft after it's been exposed to corrosive salt, and water for 50 years.
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Brad Yost
1973 T/A (SOLD)
2005 GTO
1984 Grand Prix
100% Pontiacs in my driveway!!! What's in your driveway?
If you don't take some of the RACETRACK home with you, Ya got cheated 
  
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