Little update on this project. I helped my buddy get the rearend put back together and in the car but he never finished installing it!
I'm not worried about vibrations as I've seen several of these driveshafts done (although not exactly like this one) and none have been balanced or had vibration issues. It runs perfect true, I made the tube a press fit over the splined coupler and took my time tacking, plug welding then doing the full weld. It was probably 20 degrees in my garage when I welded it, I had a heat gun on it for before and after to make sure it didn't have any temp related issues.
Everlast Powertig 225LX
Harbor Freight O/A rig
60 gal air compressor