When the intake & exhaust are mated together, they should be laying on a true-flat surface, before bolting them together and affixing them to the head. Regardless, they mating surfaces of the intake & exhaust manifolds, need to mount flat to the head. Instead of running the risk of the double gasket or sealer working, the intake/exhaust manifold assembly will be off the engine, so having it surface, is the best approach, imho.
