Just for thought, the #7 and #8 cylinders are at the bottom of the slope the engine sits on in the car, so any fuel leaking out of the carb, water, or just condensation would run down to those cylinders before any of the others. the stain its self is in the form of a puddle as it would sit in the car. Fuel stains look just like that. I'm not there, so I can't say, but it stands to reason.