It's quite difficult without a photograph. A couple of photos would really help.
Nortons were clockwise (i.e. anti-clock viewed from the points end) and used four threaded fasteners, but with pickup next to the engine. They used threaded brass bushes up until about 1940.
This is still guesswork with no photos. Rotation is incorrect, but can be altered and you'll need to custom make some threaded dowels for the BSA type of mounting.
Bearing in mind that the AC20 BSA type are probably the most common, it seems like a lot of work.
