Mr. Giant,
There are lots of good ideas in this thread. If you have done all the tune up stuff correctly and it sure sounds like you have, I think I would concentrate on the carburetor.
I am not familiar with your carburetor, but it must have a idle circuit that is separate from the mid to high speed system.
If it is ONLY a "at idle" problem, as soon as the carburetor is off the idle the engine should immediately smooth out.
Don't forget to look at motor mounts as you indicate the engine is sort of just sitting there. If the engine isn't mounted properly it might tend to hop around and make you think it isn't running right.
Sometimes you can use a aerosol can of Berryman or brake clean to find a vacuum leak. Remember to look at the plugs...they can give you good clues! Don't give up, it's only a 216.
Stuart
