Wish I could remember the year for the 4 to 6 hole change, but I can't. I used the 6-volt starter with a solenoid (not kick) on 302 for years with a 139 tooth gear. Just ran it on 12 volts. Never had a problem. How may flathead Ford have you heard at a car show with 12 volts to their 6 volt starters? let me guess....all of them.
The starter shops told me there are very few starter gears.(not ring gears) All these Hitachi starters we see for today hot rods were started in Japan on small engines as I have heard it. The 240-260-280 ZEE cars had them and they were strong enough to start our V8's. On the ZEE cars the pinion gear is the same as the one used on a 139 tooth ring gear of a GMC. I liked the 139 because it turned the engine over faster. When I started having trick flywheels made the manfacturers were haveing a hard time getting 139's so I went with 168's which are the same diameter. All my staters were for 139 so I put in the gear for the ones on the Chev V8's it went right in. When I'm at a swap meet and see a Hitachci (nissan) starter for a few $$ I buy it knowing I can just change the mount for a Buffalo 6 (Chev V8), stock 2 bolt I had made, and put in the right pinion and I done for a few $$. Good Luck
