I switched the pathetic stock horn on my GTS out for one from a wrecked X9. MUCH better! It produces a lower horn note with a less tinny timbre.
I didn't have to do too much. I bent the GTS stock horn mount back a bit to accommodate the larger horn, and used the straight bar that mounts the horn on the X9 to offset it a bit so that it would fit well. I kept the rubber grommet to absorb vibrations, and it suspends well in the cavity without touching any part of the body or coolant lines!
All in all, a simple, worthwhile mod.