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Since you are using the 7 blade fan, you need to be sure the clutch unit is engaging at idle. I'd be willing to bet the fan does not spin very fast even with the engine reved up. The STOCK replacement type clutch unit will not spin the 7 blade fan fast enough as the fan is to heavy. You need the HEAVY DUTY clutch unit. My Challenger did the same as you describe until I replaced the fan clutch and now it sits at 195* or just slightly above in traffic with a 195* thermostat. Also sounds as though you need a heat insuator or spacer under the carb



I beleive it's all in the clutch fan. My 340 started to over heat in traffic and I replaced the clutch fan and it fixed it. It can idle all day long and stay cool with AC.
Recently I have built a 446/6 pak and the cooling system is all stock including the rad and clutch fan with the "216" fan. It'll sit there and idle all day long too without overheating with the AC on! When it comes to cooling a Mopar, STOCK is best. I've proved it to my self and have heard people on here agree with me. Get a 216 fan and a clutch and I bet your problem goes away. Good luck with it.