Your Sea King was built by Chrysler You might try posting in the Chryser Force section. They may need info like electric start or manual.Magneto or battery ignition. You also could consider the tiny tach.They have a web site.More suitable as a hand held but could be installed. Uses pulses from a plug wire.Tach selected for your motor will work on any 2 cylinder 2 stroke.About $40,very easy install.