I don't know .....I have the empty cowbell there now without the chrome extension arm.....a cup holder? lol......spot looks empty without something there.....supercharger?

 

I relocated the horn between the bags like a lot do, put the Willie G skull with wings medallion it's looks great. I tryed to post a pix but won't let me

 

There is a space in the frame just ahead of the battery. If you want an airhorn you can mount the air compressor there, the horn under a side cover, and run a hose to connect the two. Worked fine on my '01 RK. Did the same thing on my SG but mounted everything under the fairing.