See pic – the first digit is not totally clear but it looks like 310. The gentleman who gave it to me said he couldn’t remember what motor it was on but I know he used to race both OMC and Mercury motors back in the 1950s and 60s. Maybe that narrows down the search.
Bob
1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
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."