Triumph 3HW MCR1 regulator box,this one has most of its original brown paint,it is dated 1 44 which is on the cover and also on the inside,I think these are similar to the 16H ones,except that the 3HW has a vee and the 16H is more oval where it clamps onto the frame (larger diameter frame tube on 16H).

Steve, according to the Lucas lists, the CVCs had identical part numbers on pre-war Nortons and smaller Triumphs. I don't imagine that they would have changed during wartime. The only rounded frame cutaway that I've seen was on a post-war dated example. Photos of Nortons show the triangular cut.