Sparker, what can I say, you have answered your own question, you don't have many options, it is a difficult job even with good workshop equipment. Left hand cobalt drill in a drill press will get it out somehow, still has the potential to damage the existing thread and this is cost prohibitive if you take it to a workshop. Put it back together with a new gasket with maybe a smear of JB Weld on both sides of the gasket around the area where the bolt is missing. Who cares if you can't get it apart in the future, it is a Briggs and they don't last forever.
