Hi David
There are companies that will convert your generator to 12V but it can be pricey. There are also 12V alternator kits to mount a Chev alternator in the stock generator position. The downside of the alternator is that it is visible on a Ford when you open the hood. The upside is that it is trouble free. For your purposes which I know are being able to drive your vehicle anyplace, anytime, I would opt for the alternator. You need minimal wiring also. The starter doesn't care if it's run on 12V as long as you don't crank it over forever. The horn also is the same. You will need a voltage reducer for the fuel gauge also.
On the other hand a good working 6V system with a good battery should start without difficulties.
Cheers,
Barry