I need some help with an old Dodge truck.

My 52 cockshutt 40 has been on 12 volts for 15 years, starter cranks faster. Wont hurt it at all as it has heavier windings to take the high amperage required with 6 volts. My 51 fargo is a different story, i put a new 6 volt starter into it and ran it on 12 volts until i did the v8 swap.