I have a 440 in my Charger and it will heat up when I'm sitting at an idle like that on a warm day. It won't melt things like you have though. I'm convinced that in my case it's related directly to air flow. I don't have a shroud and I'm running a cheap flex fan.

I still think you have a combination of problems between air flow, circulation, timing and fuel mixture. Did you ever try the "piece of paper" trick on the front of the radiator like some members mentioned?

I wouldn't think it would be too uncommon to have head temp differences between each side, not sure about a 40 deg difference though.

I'll just ask since I didn't see it mentioned anywhere and honestly I haven't read through the entire thread...have you checked your plugs to see how they look?