I agree, it's not the ring gear. Since the part you are likely to need for the starter is the unavailable Bendix (not sure this is proper use of the term but think you know what I mean) you will either get one of the modern replacements that cost around $300. Or get a used OEM Bosch. I like the idea of a used starter. They can be had on Ebay sometimes for less than $50.
Very pretty flywheel.