I just wasn't happy with the results of the HS-908 brackets, and one of the core reasons was that the Scotchbrite wheel ate the aluminum quickly and irregularly. So the part did not have square edges.
I also realized that cutting aluminum on the band saw is a total pain in the ass. So a bit of time on Google and I realized that aluminum blades are available to fit a Skill saw, a table saw, and a mitre saw. One brand, MK Morse, made some amazing claims about not heating the aluminum, and cutting aluminum squarely. Found a MK Morse CSM860AC Metal Devil 8" Aluminum Cutting Circular Saw Blade on Amazon.com -- not exactly inexpensive at $59 -- and installed it in the mitre saw.
In the meantime I ordered more stock angle aluminum from Vans. This time I ordered a 12" hunk, in case I mess up again.
Wow! Exactly as advertised. The saw blade cut the stock like butter, no heat, 10 seconds, square, and clean. :)
In fact, most of the fab time was spent sanding that last little bit down, nice and square. Sanding does heat the aluminum, so even gloves didn't completely protect me from the resulting temperature. On the other hand I was able to pick up the aluminum using my bare hands immediately after cutting it with the saw.