It depends on which end cover is fitted to your gearbox. It looks from your picture that you have a hand change box that has a foot change adapter bolted on, in which case the number will be on a flat area just above the kick start boss. Any letters will refer to the gear ratios ie CM – close medium, W – wide, C – close. Gearboxes with the gear change housing cast into the end cover will have the number stamped on the flat circular area that houses the main shaft bearing just behind the foot rest.
1946 models according to the brochure were fitted with 8” full width rear hubs and with twin 6” full width front hubs. My Brampton forks are fitted with the twin full width hub.
It’s probable that the factory fitted what ever was available, as many parts and materials were not available during the early post war period, so nothing can be ruled out!