Are you doing this for heating, or cooling? If it's for heating, isn't your basement already going to be at about the same temperature as your buried loop? I can't see how the loop and truck radiator is going to get you much, without some sort of heat pump.
Burying on the ledge is an interesting idea. If the ledge is more conductive to heat than the soil (which it probably is) it may allow you to get by with fewer loops (?? maybe... I'm no geothermal engineer).