What does this gearbox belong to

Hi, Can anybody tell me what year and model Norton gearbox belong to.

I am nearly finished collecting all the parts for a 1934 model 18 and still require the gearbox, I swapped some unwanted parts for this box as the person said it was for a 1934 but I am fairly sure this is an earlier box. But I never turn down any old Norton parts as you can use them for swaps.

The case and the front cover have the number 8265 on both items, the front cover has C5 on it and the case has a F and A as well as CR.

I would appreciate any help I can get on what this belongs to.

Regards Andy