There are no stupid questions, but, I think you can't get it backwards, because the mounting surface of the fan is offset, so that it would take extreme measures to get it together backwards, and would probably cause the fan blades to hit the radiator. As to the thermal question, I believe that all Mustang fan clutches were thermal, but the way to tell on yours is to look for the bimetallic coil on the front of the clutch, which is the side opposite the part that bolts to the pulley (i.e., closest to the radiator). It is a spiral-shaped piece of metal that expands and contracts based on temperature (although the movement might not be visible to the naked eye) and that slight movement controls the fluid inside the clutch and therefore, the amount and timing of fan lockup. In short, as the air hitting it gets hotter, it causes the metallic coil to move enough to change the fluid flow inside the clutch, and that causes it to lock up more, moving more air. Just look for a spiral shaped piece of metal on the front.