Weird 47 vibration solution

[Bolts]

Professor, is the clutch behaving nicely and working as it should? Does it chatter when you engage it and/or is it adjusted to it's extremes in order to release?
Also, have you checked the rear trans mount for loose bolts or bad rubber?
Are the motor mounts loose or a donut bad? I assume the trans is bolted tight.
Is there noise that accompanies the vibration, like whining or rubbing sounds?
Finally, is the rear end bolted down tight and is the radius rod attachment at the Y good?
I am inclined to agree with rotorwrench about the looseness of the trans pilot shaft, letting the disc wobble a little bit to get off center, but I would think you would hear something.