That motor is spec out for L4J plugs. They are no longer availible. I have been using L82C champion plugs for my 45 HP now for 8 years and have never had to change them.
Champion L4J which is no longer made--superceded by J6C no cross reference available. So equivalent would be NGK B8s or AC M42FF or M42K. Autolite 2635
