Thanks Pete,
Had an exciting day today, in the hunt for this spurious vibration around 2500-3500rpm I took the car to Vibration Free at Bicester who use specialist widgets to see where and what is causing the problem. However bowling through the countryside on the A418 a boulder hit the windscreen, frightened the life out of me and made crazy glass of the screen. Anyway I got to VF (as they very kindly collected the car on their trailer) and the culprit of the very harsh vibration was the 'new' alternator that I fitted only 3 months ago! It is the second alternator I have fitted from a very well known Triumph parts supplier, the first one just didn't charge after only a few hundred miles and this one charges but is of so poor quality it is unusable. Steve from VF said in his 20 years experience he has never seen anything this bad as it vibrated the engine/gearbox and chassis.
The upshot is apart from all the usual suspects ie propshaft/UJ's etc just take the fan belt off and see if the vibration disappears....it could be the cr**py alternators and parts we are sold to maintain our cars!!
I can't recommend Vibration Free enough, this is the second time I have used them, the first time was when they successfully identified the bell housing was misaligned. Sure enough a 'specialist' workshop hadn't fitted the all important 3/8" alignment bolt but 5/16" all round so when I put a dti on the flywheel and measured the gearbox aperture on the back of the bell housing it was over 20 thou out of centre. The limit is less that 5 thou. Try their services it can save you an expensive rebuild.
Finally is a MK2 2ltr also a 6J?
Iain