Re: 1950 12 hp Elto outboard exhaust question
It is unfortunate that I don't have the specific Elto model #s, but a model 12D10B would be a 1951-53 Gale Buccaneer Deluxe 12-horse. Substitute the "B" on the end for a "V" and you would have a Viking, or an "E" on the end would be an Elto (e.g. 12D10E). Take a look at the chart attached, and also the cutaway of a 12D10.
A few years later OMC would offer an electric start version that would have a model # like 12DE13B (12-horse, Deluxe, Electric start, series 13 [1956 in context of model #], Buccaneer). Are you sure that your model is 12ED10, and not 12D10E? At any rate, it looks like you are probably right, it could be as late as a 1953. I am curious as to why the exhaust relief (reverse) was left in the lower unit into 1953 when both Johnson & Evinrude discontinued it as being unnecessary and perhaps needlessly complicated. Gale often utilized Johnson-Evinrude castoff parts, but given that the replacement was simpler and therefore likely cheaper to produce it is puzzling. Perhaps they were just using up stock on the Gale motors; when the new 1953-54 style lower unit was phased in that probably marked the start of the next series, the 12D11(B,V or E). That is pure speculation on my part.