If you are not sure, I would start with the generator. What is the number on the metal tag. Post it here and someone will let you know. If it is 12v than your regulator should be 12 volt too.
Your starter may be 12 volt. If it is, then the starter ring gear on your flywheel will match. 12 volt and 6 volt are different. Some keep the 6 volt starter and starter ring with a 12 volt system because it spins the starter faster, but that can run into some other problems. Check the number on the starter and post it here to find out.
The wiring harness should be the same, I belive, but all your light bulbs will be 12 volt. That may be stamped on the front of the headlights.
Your gas gauge is very sensitive to 6 volt, so there should be a voltage reducer installed that will reduce from 12 to 6. Be careful with it because it will get very hot with the key on. If you allow 12 volt to go through the gas gauge with out the reducer, will destroy it very quickly.
There may be a few more, that don't come to mind just now. Someone else will come along if I have missed anything.
Are you having any problems?
