Spark plugs

RC12YC
Amazon.com: Champion (71S) RC12YC Shop Pack Spark Plug, Case of 24: Automotive

My engine builder and several mechanics I know concur.
I'm sure others have good experience with many different plugs. I have just never had any reason to try anything different.

My Champs look like this after an hour drive to a car show in my 418 stroked 340.