Copper head gaskets should be annealed periodically for best results. BTW, they rarely seal perfectly. That is why I mentioned that they do have limitations. OK for a race application where the coolant can be drained between races, as they sometimes will seep coolant out - however, they are "blowout proof" so that makes them a good choice for a race motor. Yes, O-rings should also be used with about .006" "stick out" above the deck.
Instead of copper spray try red hi-temp silicone sealer lightly smeared around the bore edges only.
