Random thought on spark plugs...
 

I have not been having any overheating issues, but I've been thinking about the coolant reroute for safety. Supposedly the back cylinders run hotter due to poor coolant flow. So...

What if you ran a step colder plugs (compared to the plugs in cylinders 1 & 2) in cylinders 3 & 4 for extra cooling to those cylinders? Just a random thought as it would be much easier than a coolant reroute...you know you are obsessed with cars when you think about stupid stuff like this at random times...:)

I think just the plug itself (electrode) runs cooler, not the entire cylinder. If the plug is running cooler, then there's less chance for detonation originating at the plug to occur. If you had another hot spot like casting flash or whatever in your combustion chamber then a cooler plug might not be much help?? But I could be wrong, I assumed this to be true but never heard or researched it myself.

I don't think the plug will have much effect on the overall cooling of those hotter cylinders, but it could reduce the chances of detonation in those hotter cylinders. I recently changed plugs in my 96, and the ceramic color was pretty uniform between all cylinders, so I don't know how much hotter the back 2 cylinders are running compared to the others.