Shorty sparkplug numbers for a 73 340?

[73Challengr]

Hi all, anyone got shorty sparkplug numbers for a 73 340?

Also (sorry, I know spark plug conversations are a pain) i'm running headers. When I changed plugs last time the 2 that are "boxed in" by the header (driver side rear) were very dirty. I do have slight detonation under power even with high octane + octane boost, I'm guessing its one or both of the driver side rear cylinders based on the dirty plugs. The other plugs looked good.

Any thoughts on running 2 colder plugs in the driver side rear and "normal" plugs on the rest? Help, hurt...absolutely no difference?

Thanks much.

[Chryco Psycho]

Accel has the shortest plugs , not sure on the #
mixing plugs can be done but a colder plug is more likely to foul .
Header / poor quality ones can make access to #5 & 7 nearly impossible .

[MoparLeo]

That is called " Mickey Mouse" Use the proper plug or as said you probably have a lower quality header with fitment issues. The factory Champion number was between RN9-YC and RN12-YC

[Chryco Psycho]

I have often used Accel plugs for this exact scenerio , it can help but doesn't off much more room , poor headers Suck .