Saw one similar at Hoar Park Wednesday Morning Bike Meet near Coventry. The owner said it just required a slight alteration to widen the frame tubes, but otherwise an easy conversion. At one time adverts for the BSAOC featured it, either as a joke or in error due to poor attention to proof reading.
Not so bullet proof...timing chains rattle, sump gauze oil filters fail regularly, but extremely good spares availability. 750 conversions turn up from time to time. Rear brake pedal is on the correct side to suit later frame and hub.
Always wondered if Beezermacc has one as his avatar, looks not to be a standard bike.
Swarfy.