Vibration Problems

[Wrenchin']

Hello Everybody,

I am working on a 30' coupe and I have a vibration problem. Here is the history of the work on the car. I had the engine rebuilt at a well known builder in So Cal. The transmission, I rebuilt with new parts from Mac's. I had the flywheel balanced, but they couldn't balance the flywheel and pressure plate assembly together (for some reason?).
I have a vibration that is noticeable at idle, really noticeable at cruising speed. It is at its worst when you lift your foot off the gas and coast. As in approaching a stop sign.
I have used a long screwdriver and listened to the engine at idle and I don't hear any knocks. I have to believe that it is coming from somewhere between the flywheel and the u-joint.
If you have any advise, thoughts, or wisdom, I'd love to hear it.

Thanks for your time,
Chris