There were two types of starter used - Autolite or Delco-Remy and they do not interchange. Each one used a different clutch housing and ring gear. If the engine had an Autolite starter, the clutch housing will look like this -
If it had Delco, the clutch housing is like this -
Notice the one that takes Autolite has a hole and bushing in the center for the starter shaft. It also has holes on top and bottom for the bolts that fasten it.
The one for Delco does not have the center hole for the starter shaft and has a stud for the top starter fastener (a nut on the stud) and a hole for a bottom fastener which is a nut and bolt.