I have the same issue with my 55 First series. It has been converted to 12V, but the starter was originally 6V and the ring gear is 139 tooth - My ring gear is very worn and will need replacing soon. My new starter is grinding about every 5th start Thinking of doing the clutch at same time if needed since labor to get the flywheel replaced will make clutch replacement "free" labor wise. The shop who rebuilt my starter said it will work just fine on 12V but run fast. the Owner was a man in his 70's who knows this starter and these old Chevy's well. What I am concerned about is if the now 12V starter will chew through a new ring gear quickly as well, even though the number of teeth is correct
