First, How hot is overheating? If you have some other issue causing the overheating (running lean because of a bad tune, problem with fuel delivery like a fuel line obstruction, lack of fuel system pressure or an air leak) adding a larger head will only mask the problem and not actually correct it. If you are running within an acceptabel temp range because of the larger cooling head but the engine is still running lean because of one of the other issues mentioned above, you will still wear out your engine prematurely.

I think you are persuing the issue with the bad shipment appropriately, just continue to email and mail him and hope he gets his act together. If you continue to get stonewalled, you may want to check with the better business bureau in thier area and see if they are registered. If they are, you can threaten them with a report to the BBB and sometimes that can help to improve customer service.