I thought that it began C419, but the highest Norton number in that sequence was C4196302..C4197736 would be an M20 and my eyesight's not that bad !
I think it's actually C4397786 which puts it in the latter part of C7353, after they had deleted the double pannier tool boxes.
The side-mounted speedo bracket actually appeared very early on. C4153287 had a centre-mount and C4153905 the offset version. This is quite early in contract C5612 which was delivered April to June 1940.
Would it be possible to find what unit the bike is from by the insignia painted on the front mudguard, done a Google search but can't find nothing similar on Canadian vehicles, it's also possible that three different colours might be painted on, which on a b+w photo make it harder to decipher.
