[Mr 42]

Start with a the Generator, you can "convert" the original to 12 V 30A. with a 12V relay
Or buy a new Alternator that looks similar to an original.

Then you have to change the Coil. If you have an original distributor, there is an adapter you can buy so you can mount a separate 12V ignition coil.

Then there is the lamp's that need to be 12Volt.
If you use the original amp meter, you need to switch the cables positions, so it shows charging and undercharging right