I am tearing down 2 Bigblock Mopars that sat in the rain for years...One a 66 440 and the other a 76 400. I mean I have to bust the pistons out of the cylinders, however....Kroil Oil...the penetrating oil that creeps really works. The valves were rusted...or should I say melted to the guides and seats..the rings and pistons were rusted...melted to the cylinder walls. Kroil oil broke them loose..do a engine search for this oil. You will be satisified...I am.