Further diagnosis; with the car parked, I put it in neutral and race the engine and the vibration is present. So, it wasn't the tailshaft bushing or the drive shaft at all.
Do you have any estimate what rpm range the vibration is at? My experience is that it will be most noticeable above idle and below 3000 rpm.
Has it been determined that engine is running on all 8 and in a good state of tune? I have worked with engines that have the balance wrong and often times it is mistaken for an engine miss. I suppose the opposite could be true.