360 engine vibration at ~3000rpm

Guys, All good suggestions. There is another piece of background I have that leads me to think checking the rear driveshaft angle is a good idea. That is:
--Since I bought the car, it had a sporadic "clunk" sound in the rear when going over a sharp bump (like railroad tracks). I crawled all under the car, tightened everything I could and replaced the rear leaf spring shackle bolts just to make sure everything was proper size and snug. But,.. the "clunk" was still there..once in a while..
---This Spring I was having a lower ball joint installed at a friend's shop and I asked him to look over the rear end while the car was on the lift. He found that the U-bolts on both sides of the rear end were not "very" tight.(though I thought I had checked them previously..?) He put an impact wrench on all of them and Lo & behold, the "clunk" was gone. Also, the car simply felt "tighter" when driving down curvy roads.
So,....it would make some sense that if the first set of torque converter/flex plates were incorrect and caused excessive vibes in the driveline, and the rear end U-bolts were a little loose, then...the driveshaft to rear differential angle could have moved. I am not sure how to verify this at home(is there a simple check/measurement to do?), OR maybe I'll take it to one of the local shops I trust. THX again, -Scott