Tunnel vibration

Just had a 2.2S spec engine installed in my 67S. I drove the car that had the donor 2.2S just before removal, and it ran/idled perfectly (other tests done as well to determine condition of engine).

After installation, I now have a vibration that appears to be coming from/through the tunnel via the shifter. Vibration is barely felt at idle, but becomes more noticable at 1200 rpm to 2000 rpm, but the vibration is felt at the spot you hold the throttle...in other words...a light pressure on pedal from idle stops the idle vibration, but if you reach 1600 rpm and back off slightly to 1400 you get the heavier felt vibration....same if you go from idle to 1800 and back off to 1600. Varying the throttle pressure up or down just slightly once the vibration starts, ENDS the vibration. No vibration while revs going up or down, and no vibration above 2000 rpm.

Prior to engine switch I didn't have this problem, and the new engine runs absolutely perfectly except for the vibration issue.

The shop replaced the throwout bearing at the time of the switch, and the clutch is a 3 puck setup. Engine mounts were deemed in good shape. We have checked for some of the obvious external vibrations (muffler etc) and have found none.

Thoughts now are to loosen engine bolts, shift engine around slightly, and rebolt and check. Then if that doesn't work, we are going to replace the clutch with a more street oriented clutch, and also replace engine mounts at the same time.

Any other ideas?

thanks,
Soterik