Kampala has it correct. Unless you have the absolute original starter (and you are positive that it was never changed by any prior owner in the 50+ year history of your car) AND you absolutely insist upon keeping "everything original", you buy a factory rebuilt from Bosch, and exchange your core.
Early on I had mine rebuilt by a local auto electric place near the restorer. Well, I think the restorer had some issues with it; we spent way too much time screwing around with it. It would work fine "on the bench" but not in the car. The culprit as I recall was some off brand solenoid or something like that...
Also prior to even restoring my car, when I was in the process of choosing a restorer, one well known restorer spoke with me and then showed me how he does business. He showed me a few pages of another Pagoda he had restored with a "work sheet" detailing what was done. Well there was a full page of detail on the starter showing how all of the 4.5 hours of labor (which could have bought a few new starters) was required along with a detailed list of the parts and machining requirements. Um, heck no.
So after the rebuilt by a local guy failed, I just bought a factory rebuilt Bosch, and turned in the core.