I was hoping you could describe the vibration a bit more. I have something that I believe is very similar and have done pretty much everything you mentioned in your thread. (ie, balancer, clutch, flywheel, engine mounts, etc).
My vibration changes with RPMs, and can be felt (shakes) in the cabin. However, when listening to car from the engine bay, it sounds fine. No knocks.
My engine had been sitting on a stand for about five years and was recently reinstalled. I hadn't thought to look for a vacuum leak, but after reading your thread....
Hey oatburner, I was just recently looking at the thread with your notch. Do you still have the wheels that you started off with that you shined up yourself? I am guessing not I see that it was way back in June that you started that thread.