Make sure the cats have an easy escape route from the dog and whatever you do, don't hold them yourself. With an older dog I would be inclined to let the cats roam the house without the dog around so he gets used to smelling them in his space -put the cats in a room by themselves once they've wandered. Then I would sit on the floor with boofhead and let the cats out, keeping the dog calm. They will no doubt hate him to start, but given time (and so long as the dog doesn't get aggressive) they will all learn to get along.

My cat was seriously unhappy when we got a puppy last year but now the dog will lie flat on his back while the cat walks all over him, licks him etc. No doubt who rules the house here!