i used a large, momentary switch from a printing press, that i mounted to a bracket on the floor in the same position as the original. it will get wired like a normal, key type, starter circuit.
Fasten your mechanism to a headlight dimmer type switch but one that single stages . Meaning it disengages when you lift your foot , or use a freight elevator type switch. Studebakers had a switch next to the clutch pedal ....