[Earlyboomer]

Did you have any way to tell at what temperature the thermostat was opening, like a meat thermometer for instance. At this point from what you have said, I would try a new thermostat with the temperature called for by Ford for your engine. The thermostat opening too soon could be why there is no heat. After warming up the engine the top radiator hose should be pretty warm, it would be hot in the summer. At this point from what you have done so far, I suspect the thermostat is faulty.