The rad will purge itself of air eve wth a thermostat installed. Most problems with trapped air in cooling systems involves conditions where the highest point in the water jackets in the engine is higher than the highest point in the radiator. Most vehicles with that design have a bleeder screw to purge them. In the case of these old trucks, that shouldn't be a problem, some do put a 1/8" purge hole in the thermostat flange to assist in puerging. I would be very leary of accepting advise from the engine builder without double checking first.
