As a Pantera guy, I'm an authority on overheating and how to combat it.
You don't mention if your overheating problems are constant, or only in specific states. For instance, if your car runs fine when going down the road at 50+ mph but overheats in traffic, then you don't have a radiator problem. You MIGHT have a fan problem, but quad fans are almost assuredly unnecessary.
Not having a thermostat is problematic. Race cars often do away with a thermostat and run a restrictor plate in its place, a thing designed to restrict the flow of water to ensure it moves at a certain pace, keeping it in the radiator long enough for the radiator to do its job. If you have no thermostat at all, the potential exists for the water to race right through the radiator and back into the engine without actually cooling off much.
Air in the system is also a highly likely culprit. In the most extreme case, an air pocket can form in the water pump, leading to very low or no flow of water at all--very bad. So a thorough bleeding of the system would be the first (and easiest) step.
Don't overlook an obvious potential problem--fans hooked up backwards. More than one Pantera has run fine going down the road, and ran okay when stationary, but overheated at low speeds--this caused by hooking up the wires on the fans backwards so that they spin the wrong direction and are fighting the natural flow of air.
Try all those things and report back and let us know what turns up?