Belmondq:
When my Willys adopted me, it already had a 12 volt battery and an alternator, so I just went with it. The alternator bracket is beefed up to assure a correct alignment, since it's much shorter than a 6 volt generator. I am still using the 6 volter starter motor and have done so for the past 6 years. My starter foot plunger is mechanical, so the bendix gear only engages when I have it pushed in. I have never really had to crank on it a lot, since the old gal always starts right up. I guess that's a benefit to my starter setup.
If I had the complete 6 volt system 6 years ago, I would have stayed with it. Like Larry said, it's worked for 60+ years!