I'm just addressing this on my swing arm 54 box for which the parts list references the earlier plunger part 3168. I'll order the later new swing arm type gear and consider I may need to change other gearbox bits to suit. I do have quite a lot of gearbox outer covers with inards both plunger and swingarm type if I can help anyone with gearbox odds and sods but those ratchet gears are always stuffed.
Very useful info that 55 BSA sheet
