From what I understand, timing on these motors is more a matter of "feel" than anything else. What concerns me about your build is the lack of consistency and the oil in the dizzy vacuum advance tube. Have you since checked the vacuum tube again to see if more oil accumulated in it? The only fluid I could see getting into that tube is fuel from the carbs, and even that should be in trace amounts. And even if you set the timing incorrectly, you should notice consistent performance issues.

I think there is an SU carb guru in NY somewhere, but I don't know if he's on LI. Maybe your carb issue is tied to the timing problem somehow?

You could look into someone who works on MGs, too, as I understand there are a lot of similarities between the B18/20s and some of their motors. I'll reach out to a buddy of mine who is heavy into MGs and used to live down there. He might know of someplace to start at least.