Whaddya think about these plugs?

At one time Offenhauser made "dual port" manifolds. They used one barrel of the carb to feed one port to a cyl, and the secondary barrel to feed a second port to the same cyl. Mostly for V-8 engines, but there were some for inline engines. I don't recall if they ever had a "dual port" for the slant six.
offenhauser dual port intake ford 300 - Bing