Tom, I recall reading in MPH that the club did do some dyno work when designing the current version of the spiral baffle muffler. The bike used was said to be a somewhat below average performer, according to observations from riding. The horsepower figures were quite low, mid thirties, but then the testers only ran the RPM up to something like 3200 RPM for some reason. A full RPM test up to 5500 RPM would have provided more info. Torque was very high at the tested speed, especially with the spiral baffle muffler installed. Torque was in the 65 foot pound range at about 3200 RPM, which explains why Vincents hold 70 MPH in top gear so easily, even when loaded right down on a fairly steep hill. It also explains in part why they are so pleasant to ride, the high torque at low RPM means you are not struggling to find the power band.
I know of one local bike which has been dynoed at 65 RWHP, (John McDougall's Shadow) but it is quite modified.