Good answers already. With two very much lower readings in adjacent cylinders, my first guess would be a blown head gasket, too. One more check before I'd yank the head would be to squirt a tablespoon of oil into all cylinders and see if the compression goes up and how far. If you get a big boost in compression, you may have problems with the rings, too. I say this because it's better to know more before you begin taking the head off. ... Good luck!!