Steve,
Most of the 427 engined cars will overheat if left idling. Is the fan on? Is the fan working? Also check the direction of the air flow. You can do this by putting a piece of paper or a thread behind the fan see which way it is pulled. The wet finger test is not good enough. It is a very easy mistake to wire the fan in backwards so the fan is pushing air when it should be pulling. If this turns out to be the mistake I am sorry for the grief we have given you.
Now for some data analysis.
What is the ambient temp?
How are you measuring the other temps? IR, Hg thermometer, thermocouple, or ?
When you say the "coolant spewing from the overflow is cold" tells me you have a radiator cap problem of some sort.
If you hook up a pressure gage (a cheap
oil pressure gage will work just great) into the water port on the intake manifold, that will tell you if the water pump is working. It will also tell you if your thermostat is opening.
Hope this helps