If it was me cooking these two (at the same time) I suggest smoking the duck as you would a chicken. Salt, Pepper, Garlic for a base and not sure what other flavor profiles you are looking to get out of it. You could go with a sweet bbq, or mandrin orange glaze. For the baby backs, the 3-2-1 method always does the trick for me when cooking at 225 degrees. But that duck might be at 250 so If you are going to cook them together, I would go for a 2-1-1 method on the ribs.