The top hole on the bell housing shouldn't have threads in it and the bolt threads in from the rear of the truck into the starter. The bottom two thread in from the front through the starter. Pickup bell housings were the same from 55 into the late 60's 0r 70's save for a few that had hydraulic clutches. I would drop the cover and make sure the motor will turn over a complete revolution checking the teeth while doing so. I f you have a bad ring gear change the flywheel if the motor will not make a complete revolution you have other problems. Also you should put new bushings in the starter these can be purchased at your local Scottish parts store.
