Kevin,
Welcome to the forum and thanks for the photos. You are going to have some good fun with that one. It bears a lot of similarities with my own A10: 2-gallon tank, QD rear hub, 1/2-width front brake, Amal 930 carb, etc.
About your engine number, I think it might be re-stamped. The area looks like it has been sanded away. The numbers are not uniform in size and are haphazardly placed. On both my A's the numbers are neat and uniform in size. It just seams to me that, at this point in the life of the BSA company, they probably own a good set of number stamps, or three. They were still quite viable and, I would think, unlikely (or less likely) to fall down at this point of pride on their flagship mark. This said, there are many guys here who have gazed upon more examples of engine numbers than I, so it might be interesting to hear their take on my theory. All that said, even if it is re-stamped, it shouldn't take away even a bit from your enjoyment.
Can't say I've been to Squamish, but I lived for a few years in Bellingham, WA and got up to Vancouver a few times. Beautiful up there. I now live outside Chicago.
Regards,
Richard L.