K_Watson
I just finished a day project of swapping the 4 note horns off of a 1992 Cadillac Sedan Deville into my 2012 Corolla S.
No drilling or electrical modifications were necessary to make this work; the factory horn was removed, a custom mount built, horns wired, and the factory horn pigtail plugged directly into the trigger side of a standard relay.
The horns are mostly hidden behind the crash bar and condenser, the bumper hides the rest.
Pictures of the horns and mount will come after I take them off for paint.
I don't have a video of before; go outside and honk your own horn if you want to hear that awful noise. 
Here is the after...
