Look for clues.
If it has an alternator you can assume it is 12v negative ground.
Look at the coil, if it has a ceramic resistor on the primary side, or a true 12v coil, it is 12v.
Even if it is still 6v you can temporary a 12v battery in just to get it started. Don't run it any longer than necessary and do not leave the ignition on unless you are cranking or running. The coil will rapidly over heat. It won't hurt the starter unless you crank too long. Carry a small battery, there is not much room in the battery compartment.
Those are easy starters, if it doesn't fire right up, something is wrong, no spark or no fuel.
A good shortcut on the fuel, carry a nurse bottle of gas, a lawn mower tank, some type container with a section of 3/8 rubber hose you can connect to the fuel line and purge out any old gas or water through the carb drain. Enough hose to sit it up on the hood.
Automatically assume the points will need cleaning.