Here is what I have learned from this site, the chevelle site and some first hand experence....
HP makes heat! If your motor will idle in the 210 deg range all day your doing good!
Next you need good cooling parts: Radiator & cap, shroud & fan (not a flex style), waterpump, hoses and thermostat.
Coolant and timing play a big factor. Water absorbs heat better than antifreeze but there are thing in antifreeze that prevent corossion and it acts as a lube for the waterpump. A 50/50 mix is the most you want but during summers heat 70% water is going to work better. If your timing is not set properly (too retarded) it will also create more heat.
So with all that in mind start looking at the hardware first. Is each piece doing what it is designed to do? Does the shroud cover the entire core? Do you have the right size core? Isolate the part or parts that are failing!
Hardware passes the test, coolant is 70/30 check your timing 10 inital might not be enough 14 inital might just drop 10-20deg from your temp at idle. Check your total timing because adding 4 at idle if you already have 38 total might not be a good idea! If this is the case a recurve is in order.
If things are cool (pun intended) when the car is moving but tends to heat up at idle think airflow or timing. Don't run without a thermostat and keep in mind a 160deg stat may open too soon and start the coolant moving before it can pull the heat from the block. You might want to experiment with several different temps to see how they react to your combo.
There is always a chance that an external heat sorce might be creating all the heat. An auto trans with the incorrect converter can heat up and transfer heat back to the engine. A mis adjusted TV cable will cause slipage and heat!
Well did I say enough? Too much? There have been so many posts on this, did I miss anything?
Good Luck, and excuse the spelling!
Camaros Limited Nor-Cal