UPDATE:
Had T4 tested yesterday. Code P0303. Cylinder 3 misfire.
Removed coil and plug: plug in good condition and correct gap; put in new replacement coil.
Took car for 5 minute run, (country roads only), to put engine under load, seemed fine. Re-tested on T4, no re-occurrence of fault code P0303. Sorted(?).
Took car late yesterday afternoon on A90 dual carriageway. Repeat, as before, of significant vibration above around 55-60 mph as described and discussed earlier on this threads.
I'm now thinking on the second part of my 2nd entry on this thread:
Do you think it is engine; spark plug(s), ignition pack(s) or VIS motor
or a tyre, wheel, bearing, half-shaft issue?
even though it was answered: "It won't be a drivetrain issue".
Might it well be a drivetrain issue.?
First stop now I think is to have a wheel alignment check.