During my career I was involved with investigating some wobbles. There are lots of things that can contribute to the problem. I personally experienced wobbles at speed that were rather unsettling. The ones I recall most clearly are… flat out in a straight line at 220 kph. The fix was improved swingarm bushings. The other was on a touring bike and the wobble forced me across the two oncoming lanes and within a hair’s breath of the guard rail and cliff below. There was more than one reason for that one, but it also included the swing arm area.
How rigid is the Vincent stressed member engine setup, RFM pivot , etc? If all isn’t well there, then a relatively innocent shake of the bars from the road surface could build into a crescendo that is unrecoverable. Just my opinion, but I would be keeping an eye on other things as well.
Never had a wobble on a Vincent. I did crap myself once when I was going through a sweeping right hander at speed when it popped out of gear. Instant under steer as it quickly drifted towards the guardrail.