The SLS front brake lasted to Chassis number 11548, so yours should have one. I have a genuine seat for mine but it needs work.

Yes - I'm not convinced that Honda were any better organised than any other manufacturer when it came to using parts. I have two early style front fenders but neither is alloy. One had a numberplate on it which I could date to October 1961.
I think it's amazing that we have unearthed three 1961 CB72s that were probably made on the same day and arrived in England on the same shipment, all painted blue. They will have to be reunited one day...
G