You need the engine numbers in order to get the proper head gasket from Briggs. I questioned using the Graphoil gaskets as opposed to the gaskets that had the fire ring with tech support at Vanguard. I was assured that the Graphoil gaskets were the proper ones for my engine so I went with them, so far so good. Both my heads were warped and if you didn't resurface yours I'd be looking in that area. There is a how to in the tech library on how to do it.
Edit: link to how to resurface your heads.
http://mgonitzke.net16.net/tools/headgasket.pdf