Umm, white residue? It is better if you could post some pics of what the cap looks like.. Also if it really is coolant then you need to figure out what is wrong, however most likely it really is something wrong with the head and not the head gasket, because if it was a gasket you would see smoke pouring out of the exhaust pipe. The only way to be sure, post up some pictures so we know exactly what it looks like and the only way to know what exactly is wrong with the head is to take the thing off. And examine it.
PS. Are you considering swapping the engine with a larger one? or are you going for the fuel economy?
-Artem