Re: Best lead substitute for a mid sixties merc?
I had a 1966 Marktwain (150 Mercruiser) that dad bought new. I sold it in 2005 and it never had the head off and ran just fine on whatever gas we put in it for all those 39 years.
Don't worry about octane booster. Just make sure you have it timed correctly so it doesn't ping.
Cheers,
Rick