All standard size Delco automotive generators from the 30s up to the 60s in 6v or 12v used the same shaft size. .650. The exception to that would be a larger oversized generator. The larger units had a larger shaft size but cant remember it off the top of my head. If you need that info I can measure one tomorrow for you. I can look it up and see if the Delco book tells me what your Divco had on it originally and get back with you.
Ken