Dave. Sprite was very successful during the late 60s with a lot of good wins in the UK with riders of the calibre of Terry Chalinor, Terry Ledbitter and Vic Eastwood racing them. Usually using Villiers, Husky and Maico engines. They won bugger all to my knowledge in American Eagle and Alron guise, mainly because they just plain weren't very bloody good. By 1970 they were obsolete and poorly made, typical of just about everything British by then.
John, the Hipkin quote comes from a clipping from 1969 Jonesy produced from somewhere. I missed a follow up sentence to the " All the motocross frames are made from 1.5mm, 1" diamter ERW tube" quote. Frank notes that " late 1968 we changed over to mainly mig welding" which is fairly obvious on the fastback frames I've seen. My and Alans pre fastbacks are both brazed so going by Franks statement, they must have been made prior to '68.