I don't know exactly when hydraulics appeared successfully on bikes. I suspect most Vincent owners would not want the "looks".
Although, I thought that hydraulic cables might have some appeal:
Vincent brakes, not having anchor tabs, are a little more difficult to accommodate. I would think that the twin leading shoes might be a better candidate for hydraulics.
It surprises me how little engineering information seems to be available on mechanical drum brakes considering how long they were used on bikes.
David