Hi Chris,
It is usual for the arm and cam to not be in separate pieces, but on some works bikes there are variations. It is of course an Enfield component, fitted to many different makes, including Brough Superior, Norton, Zenith, etc., as well as Royal Enfield. You will see different fittings on these different makes. Vintage and early 1930s Flyers and Reps with the right-hand side brake pedal had the gearbox tray with a groove milled into the side to give working clearance for the brake rod. When foot gear-change came in the brake pedal went to the L/H side, and so the gearbox trays no longer had the groove in them. Maybe you have a later tray that is causing the clearance issues ?
Brian
