Have you checked compression and valve clearance and that all spark plugs are firing...?

Could be out of balance flywheel

Has to be internal on motor. As I have started motor up with clutch and pressure plate removed and fan belt removed and free reving the motor still has vibration.

Could be a badly balanced flywheel, all the way through to a cracked crank (bought one of those once). Or maybe the clutch plate is worn badly or it's the pressure plate. Hopefully for you it's an accessory like an alternator bearing, or a broken mounting bolt you just haven't found yet, like the alternator bolts.

That should have said pulled an L20 apart

Check the little metal straps that hold the pressure plate to the clutch housing.
Pull an L20 apart one weekend looking for some vibration.
Turns out it was these things bent when I missed a gear when racing.

Or uni joint in the tail shaft?

Bulge in a tyre shows up in roughly that speed range

Yes it does. But it only vibrates at the rev range. So smooth as below say 2500 then it vibrates real bad to about 3000-3500 then stops

could be a leak in the intake manifold somewhere affecting compression. i had this issue last time when cracked my manifold while mounting it. it would run very rough upto 3000 rpm but run ok above.