This is a great thread and jkust about all of the options have been covered here. Just a few more things to consider/check if the things already listed don't do the trick.
1) Is your ignition timing set correctly. If you retard the timing, any motor will run hot. If your headers are getting very hot or burning off the paint/coating, its often an indication of excessively retarded ignition timing.
2) Was your engine built with underdrive accessory pulleys? Can you get an overdrive water pump pulley? Engine builders often use underdrive accessory pulleys on performance engines to gain a little more power and to avoid over reving the alternator at higher PRMs. This is almost never a good idea on the street as the engine does not circulate enough collant at low speeds. You can tell if you've got underdrive pulleys as the pulley on the damper will be smaller than the water pump pulley. If this is the case, I would suggest switching to a standard setup or even an overdrive setup (water pump turns faster than the crank) if you can find one. I used this trick on a blown smallblock in a Vette (which has limited cooling capability) at it improved the cooling situation at low speeds by a noticable amount.
