Shakes or Wobbles problem
1983 Ford Mustang 6 cyl Two Wheel Drive Automatic 150000 miles

I have a 3.8 carbureted V6 with a C5. It had a vibration at idle that suddenly got worse. At first it was minor and only noticeable at idle. Now it shakes the whole car whether its in gear or not. I've swapped this motor from another car I have, didn't have the vibration then. I had put new plugs, wires, rotor and dist. cap, and it does not "feel" like an ignition miss. I put a new harmonic balancer and no change. I have new motor mounts also. At idle it vibrates the worst at 1500 RPM, putting it in gear dampens it, but you can feel it at any speed while driving. I checked the conv. to flex plate nuts, they are tight. There's no mechanical noise (like rod knock or anything). Would loose flex plate to crank bolts cause this problem? Any ideas on what to check? Transmission shifts fine, no problems with starter alignment