I had oil all over the front and back of my cylinder and bike. I pulled the head and had to hone the mating surface flat. The head gasket showed signs of escaping compression front and back.
To hone the surface, attach a sheet of cloth backed 240 grit sandpaper to a piece of glass with spray glue or other adhesive. You can also use the kitchen counter or table in a pinch.
Lightly hone the head surface and see where it doesn't shine from the honing. Keep honing the head, turning it a bit with each swipe. Keep the pressure low. When the entire ring is polished, you're done. You should also do this to the cylinder mating surface.