To get the bracket installed, I ended up bending the bottom mounting tab 180 degrees to utilize an existing hole. Before I rotated it, I used a grinder to make the tab thinner so that it would fit inside the radiator support arm. After I got it to fit inside radiator support arm, I realized that I didn't have room to drill a hole with my winch control box in the way. Having no idea the best way to do it, I heated up the mounting tab with a torch and bent it 180 degrees. I was then able to use an existing hole. I did cut off one corner of the mounting surface to give additional clearance to the horn, and shaved a corner of a mounting tab because it was going to rub on a raised part, but it looks like I didn't actually need to do that.
The bottom mounting tab bent 180 degrees. Not the best view and don't have a better pic. Sorry!
In the end, I don't think I needed to trim the edge of this mounting tab. When I was mocking it up, that bump to the upper right seemed to be interfering.