Hi Folks,
Done a bit more playing, took Martin's advice and changed the bearings, once removed they did have a slight rock in them (movement).
Then changed the pulley with the supplier, same out of alignment with a new pulley assembly(TaperLok), ditched that after numerous failed attempts to align with the locking grubscrews.
Rebushed an old pulley to be a pull on fit using the M8 threads in the end of the motor shaft, but there was no keyway in the pulley, so used doubled up dogpoint grubscrews through the sheaves into the shaft keyway, ran the motor on the bench, but still a lot of vibration at full revs even though the pulley ran true.
Scratched my head several times over this issue, but worked out that replacing the key with grubscrews might have upset balance, so drilled the pulley outer face opposite the keyway several times during a trial and error exercise.

Managed to get it running very smooth at full speed(60Hz), but there still seemed to be frequency issues at differing speed ranges, so back to trying the VFD carrier frequency (PD041), I'd left it at a new setting of 3 out of a range of (1-15), I tried working backwards towards 1 as going higher just moved the vibration range higher, I ended up using a setting of 1 with quite good even running throughout the speed range, but now I have a slight whining, which I can live with.
When I fitted the motor back on the lathe, I then had issues with the very long run belts, giving a vibration of their own, so it looks as though my thoughts of earlier fitting the motor onto the rear of the bed, below the headstock, are going to become a reality.
Also amongst this saga was the belief my headstock bearings might need adjusting, I posted that I'd used a test bar to line the headstock up, but hadn't really tried any serious unsupported turning, well whilst faffing with these latest problems, the turning an unwanted taper issue reared its ugly head, so set about adjusting the headstock to turn parallel, this took several trials, removing change wheel quadrant etc, slackening the 4 capheads (the front one is really awkward with the gap piece in place), but after 3 attempts got it to turn a 2" dia piece of En19T nice and parallel, with either a 0.002" or 0.025" cut applied using a DCMT 11T302 tip, the finish was mirror like.
So now a happy bunny on the turning bit, still have to move the motor though…
Bernard.
Edited By Bernard Wright on 10/06/2016 01:29:04