Miked raises an interesting point. Are these Mk2 Amandas? If you watch the film carefully you can see the cylindrical fuel tank which looks like those fitted to the Vincent 2-stroke engines. Also the handlebar arrangement and lifting handles on the hull are very similar. Far more attractive riders, by the way!
The late Alan Rennie related that during his time at the Works, people with truck driving experience were sought. Alan had had some and soon found himself shuttling between Stevenage and North Wales where Vincent's had established a facility to produce the fibreglass hulls. These were brought down to Stevenage to have the mechanical bits installed. He said that in the winter that journey was purgatory as the truck had no power steering, a crash gearbox and no cab heater.