I would say that the Gassers reached the peak of their popularity in 1965. Starting in 1966 the AWB match racers began eroding this popularity, and by 1967 the flip-top funnies replaced them in the hearts of the fickle ticket-buying public.
What sort of cars? Jeez. Depression-era anything, post-war Anglias and the like. Coupes, sedans, panels, pick-ups, you name it. Rarely Fords, though, because 1) the carcasses of the other makes were cheaper and 2) the hot-rodders got to them first anyway.