Thanks John. I have original BSA issue parts books covering "A" group from 1949 to 1960, the RGS supplement dated Feb 21, 1963, Roy Bacon's BSA Restoration, and Bacon"s BSA Twins and Triples. All useful in their own way, but none give details like you just did. The drawings in the parts books are great, but they don't list dimensions. Just dawned on me: I was looking for part numbers on the outside of the brake hubs. They would more likely be inside. I'll have a look tomorrow.
If anyone needs part numbers, like I said above, I have what looks to be the complete collection of A7/A10 parts books. Be happy to look them up on request.