I'm going to venture that these part #'s are the same thing, but pre-adjusted to fit the specific model:
82710142220 is for e46/4 (sedan)
82710142221 is for e46/2 (coupe)
I bought used OEM roof racks ($140 C/L) that came off a 5 series car, but the brackets can be moved so they also fit the E46 series. Getting them adjusted spot on took a while, but now that it's done, they install very quickly. Make sure you get the wrench that's keyed to the unique bolt head. A new wrench and 4 bolts is about $70 from the dealer.
The front and back OEM racks look identical, but they are not. The front rack has 3 small wind spoilers on the bottom side of the rack to cut down on whistling.