I had a very similar problem, the PO had installed a 12v starter designed for the 168 tooth (6V) ring gear. I solved the problem by installing a Napa part number 244-9657, 6V remanufactured starter with the 9 teeth, 1 3/16" OD gear, ($96), removed the 6V solenoid and installing a BWD S92 ( Delco D289A) 12V solenoid ($49). The 6V starter will work with the 12V system just fine, it'll spin nice and fast. I had to re-work the copper strap. Many bolters have said that you don't need to change the 6V solenoid and it will work for a very long time. Others have said the 12V causes the solenoid to "slam" forward with a potential for damage to the starter or flywheel. Me, I just changed it out to be on the safe / sure side. Questions, PM me.

Ron - - Dusty53
1954 Chevy 3604
In the Gallery Forum
"You can't dance with the Devil and then wonder why you're still in Hell."
"They will forget what you've said, and they will forget what you have done but they will never forget the way you made them feel."