Hmmmm??? You put oil in the top, through the valve cover oil inlet, it must be something in the head that is letting the oil enter the cooling system? Did you have head work done? You didn't forget to put the head gasket in did you? (not sure if that would make a difference) OR maybe the front crank seal?
I would check a schematic of the gaskets needed and think REAL hard if you put each one of those in that motor!! good luck.