As far as I'm aware there isn't a guide to the serial numbers, so no real way to figure out the year of the early motors. Most of them were sold as kits, It is my belief that the motors were all built in batches and sold over long periods of time. So a motor that was built in 1910 may not have been sold until 1915. But that is just my theory on these. The later models with the clutches and magneto ignitions you can narrow down slightly, but not a specific date.
Any chance this one is for sale? I'm always looking for spares for my Shaw.