I dug out a spare Delco-Remy starter motor. This is a more modern one, nomenclature is stamped into the cast housing and reads as follows:
1107399 6 M 12
The gear in the housing is straight cut, it should bolt right in place after the cover is removed. Gear will mesh with clutch flywheel.
Use care when fastening and tightening the starter housing to the clutch housing, the flange edges on the starter housing can break the corners off at the bolt holes. The starter is heavy, might be best to bolt housing first, tighten down. Given the age of these things, I'd also recommend using an appropriate tap, thread chaser on the holes, always good measure, that ant anti-seize. The spring loaded switch on the starter motor operated by a lever, will seize if left in the elements, best to try and keep under cover if possible, lubed etc.