I would probably wire in a small toggle switch and put it on the bottom edge of the dash, below the light switch panel. It would be a momentary spring loaded switch that would not let you start (turn over) the engine until you actually hold the switch and close the contacts. As soon as it starts, and you let the switch spring back it will not engage if the key is turned until the switch is again pushed to allow it to start. This is a manual means taking place of the clutch safety switch. Yes those originals are hard to locate, bet brewers would have them though.