AS a quick and dirty - I don't want to put more time/money than neccesary into it - move, you could try one of the head gasket sealing products. That engine isn't very high compression is it? Might be worth a shot, but I'd bet against it working.
10:1 compression, it's a for-LPG motor. I'm thinking a few rounds of head removal, etc. are called for first. I could always shellac up the old thicker head gasket and see what happens. -- Jim