I would contact either altrider or black dog cycleworks and ask them directly. I also have a 21 GS and was starting to look into what crashbars and skid plate to go for. I wanted all to be same company to avoid fitment issue. That would leave me with H&B or Wunderlich. And I know BDCW goes with the H&B bars as they sell them. (Altrider still has not released their crash bars yet) In your case though a direct call for verification would be best.