If that's a newer mustang, I believe that space is actually a doubledin. It's just because of the wierd way Ford does their dashes that it's a little harder to mount things in there..
I'm trying to think of where you could move the AC stuff to, but i'm failing. I think the mustangs still use mechanical controls, so you can't go too far..
Good luck with everything though, and let us know how everything goes!