Can anyone suggest what the thread is where the advance retard cable screws into the magneto body (Lucas M01)? At first glance its about 7/16" diam and 26tpi. BSCy ? Its not the cable thread that's stripped, that would be an easy fix, but the female thread in the magneto body!!!
It's simple to change that end part on an MO1. Is an MO1 the same size as the original type for a B21? I assume it would have had the pre war ring cam type? Just wondering if that might be your carb fitting problem?
That threadform sounds right. Can't you borrow/buy a BSCy tap, clean up the thread and Loctite the fitting in?