The DeeZee Aluminum Headache Rack with Sliding Load Stops, part # DZ95050RB, has aluminum brackets.
As for modifying the headache rack, you can certainly do that. Most anything can be cut/welded to suit your needs. Of course, this will void your warranty as you said, and there is no guarantee it will work or perform they way it is designed to. In other words, you can but it's risky so I can't recommend doing it. view full answer...