remove the starter and look into the cavity where the starter meets the flywheel and look for missing teeth in the flywheel... they are probably in there someplace(the missing teeth from the flywheel, look for missing area on the outiside of the flywheel.... then you have proof that the flywheel is bad... i had this years ago with a 66 mustang...i would just put another starter in it as you could drive up to a parts place, open hood and lean over and remove two bolts and one nut for the wire on the starter, bring it into the store and swap it out for $20.00.
i would last about 3-4 months.. then i learned that the starter drivew could be replaced.. they cost about $8.00 at the time...... worked great to let me use the car and then i rebuilt the engine and bought a new flywheel for $25.00 from a ford dealer(this was back in 1973).....
