In my experience (don't start shooting at me yet) if you put the smaller flywheel in the bigger bell the starter will not even touch the flywheel.The distance the starter is moved out in an arc is much larger than the lenth of a flywheel tooth.

I've always used auto starters with auto and standard starters with standards. Funny the 351M 351W and everything but the 400 and 460 show a different part number in the LMC catalog for auto vs standard starters.I laid in a friends snowy driveway one Friday night and put 5 starters on a 351W till I got one that didn't grind the teeth It was the only automatic one he had.I know where it came from cause I pulled it off a car.Just my thought but try an auto starter and a standard starter from a 351M .Why would a 351M call for different part # starters and a 400 and 460 not?They bolt to the same transmissions.