Hi machiasmort,
70 MPH on several dyno runs. 68 MPH on the "Roller Road" [MPH dyno, Portland, IN 2005]. 66 MPH on the street checked with GPS & digitial speedometer.
My 1950 Sportsman managed to travel 150 feet [dirt drags] maxing out at 40.3 MPH @ 8220 RPMs [not bad for a flathead], and easily bested some wild OHV Whizzers.
I currently hold all the speed records except for one, Bonneville "twin vintage Whizzer powered". A friend of mine, Roger Brophy holds that record.
I hope to run my twin Whizzer powered bike at Bonneville in the future, but will be using 2 new edition SE motors. The 2 engine Whizzer was built by Ron Dow [Texas] and donated to me by Terry McAllister [recently left us for a better place].
The twin powered bike managed a little over 60 MPH on one motor.
Have fun,