When I tried to install the horn I found that I could not install it using the stock bracket because I couldn't get the the horn level and the bolt through the bracket at the same time.
So, what I basically had to do was get a piece of metal about two inches long (1 inch wide and very flat) and drill two holes in it with the holes centered about 1 to 1.25 inches apart.
I then installed the new bracket with a bolt and a locking nut, and was able to then install the horn using the mount attached to the horn.
I was going to take a picture of everything, but by the time I had everything lined up so I could take some quick photos as I installed the horn, I found out at that time, that my camera battery was low and the camera would not let me snap any pics. Seeing as how I had three hours into the install, I was not about to wait for the battery to charge.
I hope this helps. I know that some people have managed to install the horn without the bracket, so maybe they will share what they did.
Yellow-Smart