I looked at the Old Outboard Handbook which lists the 1940 year serial numbers 355,972 thru 397,900 and your serial number falls within that range. The same book shows the 1940 motor as a PO-10 and the PO-15 model starting in 1941. This serial number listing has been proven wrong before or it could be the model number listing is wrong and the PO-15 started production in 1940. If yours is clearly labeled a PO-15 (and it sure appears to be one) it’s either a 1940 or 1941 model.
Bob
1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20
“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."