Yeah, It looks like the thermostat just sits on the rad....
yes, unbolt the rad and take out the thermostat and mark/note witch way it sits+the way it faces(on a car it has a little loose pin). Then bolt it back on minus the thermostat, fill her up w/ water and
you should be able to tell if it overheats in 5-10 min of it running without the thermostat. If it doesn't overheat/get hot real fast then it's the thermostat because the water is flowing to the radiator and through the engine
It is just like a thermostat in a car....The thermostat stays closed until the water in the engine reaches a certain temp...you can take them permenantly out in a car. It just makes the heater get hot faster with it in.