In 1948 (and later years), a 6v solenoid starter was used on DD (step van chassis) trucks. In 1954 (and later years), a 6v solenoid starter was used on Hydra-Matic equipped trucks.

Foot pedal starters were standard on manual transmission 6 cylinder trucks up through 1959. 6v was used until mid-1955 in Chevrolet trucks (Task Force trucks were 12v).

I do not think you can remove the electrical solenoid mechanism and replace it with the mechanical foot pedal mechanism (but, I am not sure about this)