The Op asked if the stomp starter was only used on 6-volt starters. 12-volt stomp starters were used on early Task Force Trucks. Yes, a 6v starter will work on 12v. The thing to remember is the ring gear you use must match your choice of starters. If you want to use a 6v started you must use a 139-tooth ring gear and if you want a 12v starter you must use a 168-tooth ring gear. The 139-tooth ring gear was used up to 1955 First Series trucks. (Advance Design) The 168-tooth ring gear was used in 1955 Second Series and later trucks. (Task Force)

1954 Chevy 1300 engine 235 (1959)
1955 (first series) Chevy 3100 engine 261 (1957)
1927 (other brand) Model T- engine 327 (1968)