oil pressure light

I just got a 1998 3.4 olds looks light it might have a coolent leak or blown head gasket rear head . oil was clean with a 1/2 cup of of coolent in it. changed oil started motor ran 2 min motor was missing i noticed oil pressure light on i did not check oil sensor yet . i know i will have to do heads and manfold motor has 94,000 miles on it it was not run hot and there is no bottom end noise. any help suggestions on the oil pressure. also what are the best head gaskets to use dealer oem or what brand other then felpro.
thanks twharley