I am not fond of the cork gaskets, since they always seem to leak. There are a lot better products out there that are made of synthetic rubber compounds that stand up to the heat and oil better. If you are going to use the cork ones, then consider Permatex on the valve cover side to hold them in place. Something such as Permatex High Tack will work well. Just don't put anything on the head side, since it will be a problem to remove later one, when the valve cover gaskets start to leak. The nice thing about the rubber compound ones, is they can be re-torqued if necessary, but usually when the cork ones leak, it is time to change them again.
Cadillac issued a service kit that was a heavy piece of steel that had a slight curve to it, and it was placed under the valve cover bolt, and this distributed the torque a more evenly across the entire valve cover area. One thing to keep in mind is that you don't want to over torque the valve cover bolts, and break one off.