To summarize, you have a mechanical pull rod to the starter, 12V battery, negative ground, distributor & coil ignition.
Do you have an internally regulated alternator? If so, does it have three wire terminals, or just one. The common conversion is to three-wire with a shunt from the sensing terminal to the battery terminal on the alternator. If it is, look at Bob's drawing in the link and see if you can hook yours up this way.
I don't know if you need to get a new light switch. I would think that you could find a way to just convert an original to "on-off" function. You would need an ohm-meter or 12V test light to confirm that you are using the right terminals.