For those that are interested in various ways to mount the Norton gearbox here is one way. It is on a racer, so the inner primary is a simple 1/4" plate. The F106 has its legs sawed off. Although this particular set-up has some modifications, I think it would work with a stock primary cover. When you make your own plates you can modify the relative positions of the gear box, the engine and the swing arm, which was done here.
David
David