I would just keep Stockpile, because using Spit Up/Swallow will lower your defenses after being used. As for your set, I would use the Baton Pass set, which consists of Baton Pass, Stockpile, Substitute, and Shadow Ball. You could try for a sweeper set, but Drifblim has a measly speed stat of 80, so it's bound to get outsped and knocked out with 1 or 2 attacks.
Hope I helped!