I did get a chance to chat with Smokedawg. He had a 180 at one point and it still overheated.
I think an aluminum radiator is probably the best bet at this point. The only other thing I can think of is that there are air pockets in the water passages. When it's cold, pull the radiator cap off. Start the engine and let it run until the thermostat opens. Water level shouldn't drop much. If it does, you probably have air pockets. Top it off and close it. Oh, also, turn your heater on full when checking water level.
I take it that once you start moving that the temperature starts to drop significantly?
------------------
351W 89 Mustang GT Convertible