On very few tractors do the bendex and ring gear engage completely.
i have split many tractors (of different brands)with worn out ring gears and simply removed the gear and put it on backwards. never had a problem with any of them.
I know Ford had two different armatures. The difference is about 1/4 in the lenegth of the shaft.
My 9n is on 12volts. I've never had a problem with the ring gear. it did break the bindex spring.