Standard is copper and the best conductor- should offer the best performance and lowest price. The advantage of the platinum and iridium tips are longevity, you’re usually best served running the copper and replacing them more often.

Some have indicated that the Autolite 764 is discontinued.  They can still be found, especially on the internet.

The Autolite 104 is the replacement plug for the 764 and is basically the same plug -- 104 has full threads on the body and the 764 is threaded halfway.  Either will work.  (GT-40 or GT-40P heads)

What is the difference between full threads or half threads? Does one run cooler than another?

Yea I know… my cousin has the same boat except an 1998, and he has never changed plugs either! He has 400 hours on his and I have 500 on mine. I was thinking when changing them to soak the threads with kroloil for a few days…..

That being said we are checking driveshaft alignment and repacking the rudder and drive shafts this spring! Any tips on those projects?

Autolite spark plug prefix list:

I figured that was the case, I guess with the more confusion, get people to buy the wrong stuff the first time around, and then after they come to a place like this, they find out what they really need! I will go to my local car parts store And support something local!
Thank you for clearing that up, I know spark plugs make a difference. My Evan tech has indexed plugs. That’s a whole Nother topic. This place is an underrated source of information! Thank you everybody