The Model A works just fine on 6-bolts. However, there are some good arguments for changing to 12-volts. Twelve-volt batteries are not readily available at most auto parts stores. There may come a day when they are no longer available. Modern gadgets need 12-volts for recharging, cell phones and the like.
During the conversion it is best to re-wire the ahooguh horn as the dropping resisters will burn out with repeated use. The attached article is how to do it.
http://www.santaanitaas.org/wp-conte...orn-to-12v.pdf
Tom Endy