Jonny, smoking baby backs at 3-2-1 is too long. That time is for spare/st. Louis style @ 225*. At 225*, the rule of thumb is 2-2-1. I actually cook my baby backs at 260-275* and the time is even less. I also don't foil for the middle 2 hours as I don't like the texture and the FOTB results. If you are cooking at the much publicized 225*, the unfoiled time could be about 3-1/2 to 4 hours until they get a good bend, then about 20 minutes for sauce/glaze. There is a lot of room with ribs for personal preferrence.
Good luck and let us know how you come out, Joe