68 Dart 440, ez heads,griffin rad,hhr fan,mancini 7 blade pump.Sitting idling in the driveway 185 deg,drive around the block hits 210 deg.Drive to the other side of town hits 220, shut off boiled over!!!

I assume you have a big rad... you might have air in
the system

My car does almost the same thing so I suspect that a 19"radiator is not up to the task
I have a 493,EZ heads,Mancini rad,CV electric pump,HHR fan,180 stat,Mancini pump housing.
In my years of being an auto tech. overheating on the highway means not enough flow through the rad or not big enough rad
I have yet to drive mine in less than 90 degree weather though
I will have time to get out in the cooler weather this weekend so lets hope it's just the extreme heat
Gus

Make sure that all the air coming through the grille has no where to go but the Radiator. Seal off all holes, gaps, and make foils or air dams to direct the air through the rad.
Distilled water only during the Summer months with a bottle or two of Red line Water Wetter.
Check your timing. Fuel pump for lean conditions. Spring in the lower radiator hose. Thermostat for sticking conditions. Bleed the water system of trapped air by loosening the temperature prong nut while filling up the radiator. Check for clogged radiator.

Well the tune is good but just a little on the lean side so I have since jetted up after the plug read.
The cooling system is all brand new this year and I have no air in the system(I use an Air Lift tool to fill the cooling system)and the hoses are new with spring inserts.There is however a lower shield that fits below my core support that I left off the last time I had my bumper off
Thanks
Gus

You have air in the system as Mr. p body said. The proper way to fill a performance cooling system is to fill the radiator to the neck, put a jack under the k-frame,and raise the car 1 inch. Turn on the electric water pump and slowly fill the neck as the bubbles come to the surface. Jack the car 1 inch at at a time filling the neck slowly until there are no bubbles. When you can not jack the car up any higher, now do it even slower until only coolant passes the top of the neck. If done properly, you should add an additional 1 quart to 1/2 gallon of coolant. My cuda runs the 1/8 here in Texas in 100 degree in day and 90s in night. It comes back to the pits about 180 to 200. I use a Dodge Caravan (small) radiator with about 3 gallons of coolant. Keep the carb fat and run plenty of timing in hot weather.