There's another option, although it might take a little creative wiring. It's possible to set up a "series/parallel" electrical system, using two 6V batteries, that cranks with 12 volts and recharges the batteries and runs the other accessories such as lights, heater blower, radio (if any), etc. on the original 6V system. The concept was used on Diesel engine trucks for a long time, running on 12 volts, and cranking on 24. I'd have to do a little research and maybe spend some time at the drawing board to come up with the components and circuitry to wire a 6/12 volt series/parallel system, but that would allow you to install a 12V starter and still run an almost original-appearing electrical system. Just food for thought- - - -switching to a straight 12V electrical system isn't that difficult, but it does involve buying several new parts- - - -alternator or generator, voltage regulator, ignition coil, all new light bulbs, voltage-reducing resistors for the gas gauge and heater blower, etc.
Personally, I'd much rather just change the flywheel- - - - -lots less work, and probably less expensive!
Jerry
