Well, after some searching of the internet, I have enough information for the mechanical timing, so that is good news.
Experience is gained by learning from mistakes as well as successes!.
My guess with the ring gear is that there is sufficient tooth profile to give a signal. And that the broken teeth are not adjacent, then any signal anomaly is not so great. It's essentially the same principal of detection as ABS teeth on drive shafts, and they generally work under much worse conditions.
A flywheel/ring gear is not so expensive, new. And ordinarily, I would just replace it without thinking about it. But I have to keep in mind the mounting cost of parts required to keep this engine viable, compared with buying a short engine.
