Thanks for your note. I'm glad you found the tutorial helpful.
I made the angle bracket from some 1/8" thick aluminum flat bar stock from a local hardware store. It's easy to bend (using just pliers) and drill holes into (using a hand-held power drill), but strong enough to hold the horn rigidly in place once it's installed. I also found that using such material allowed me to easily customize the bend shape and the hole placements to my personal preference, rather than trying to accommodate the pre-drilled holes in a ready-made steel angle bracket that I tried on for size earlier in the process.
I hope that helps. All the best Jeff, and may you never have to use your horn in anger!