Pay no attention, RBT.
Sadly that transom bracket is late forties to early fifties.
The one that I think is the standard stern transom monted bracket - ie not for military use - is this one:
And this one - although the caption dates it as 1939 it is actually an advert from 1946.
The one we just don't know about - and which the other Charles is possibly thinking - is this one here:
But the one above is an OP, and we know that had a different shape bracket. The one in the picture is a chunky bronze affair rather better suited to the military knockabout use. But there are so few they could be post war add-ons.
(Actually I've just looked a bit closer and it's not an OP at all. It's got the wrong tank, magneto cover, tiller arm, cylinder block, carb, crankcase lower half, and so on....)