Reply to "Thermostat or not ???"

Depending on which water pump you have, with no thermostat, the car will overheat. The 3/8" hole in the brass washer under the thermostat leads to a radiator bypass circuit for quicker warm-ups. The 351C thermostat has a little plug on its bottom that enters that hole at full-open and plugs it. Otherwise, 25% of the water simply bypasses the radiator, and the Pantera's cooling capacity will not absorb that. Some aftermarket aluminum water pumps like Weiand do not have the bypass passage cast in, so in that case, any thermostat will work. But for all other cases, you need a 351C-specific thermostat.