 Dunstall successfully developed 500, 650 and 750 versions, later producing a Lowboy frame kits sold to the general public.After the Dunstall organisation closed in the early 1980s, other specialists offered the Lowboy frame.Having earlier installed the Dominator twin-cylinder engine of 500 cc and 600 cc, in 1959 Norton put the old single cylinder Model 50 (350 cc) and the ES2 (500 cc) into the Featherbed frame to rationalise production.