Since you need a new starter, buy a 12v conversion starter such as this one
[Click] from Classic Parts.
If your wiring harness is in decent shape, you can make the change over to an alternator with a few wiring changes, otherwise you can purchase harness made for 12v and alternator’s from most vendors.
You’ll need to change all of the light bulbs including your headlights. A quick search using Google will find many articles and videos on how to change from 6 to 12 volts such as this one
[Click].
This change has been made by many of the members here on the “Stovebolt” forums so if you run into any obstacles just ask!