MAKE SURE YOUR BLOCK AND HEAD ARE COMPLETLEY FLAT, metal and copper gaskets have a much less flex/crush rating compared to cork/fabric/ rubber ones, what ever they make it out of these days.
I think copper has a flex/crush rating of 0.001 of an inch which isnt much and the metal ones are even less. So to have a flat block and head is critical, other-wise your going to be undoing the head again.