Jim, is your dash commercially done? It's a beautiful piece...
I did my firewall with a 1 inch diameter wire brush on a cordless electric drill. I have used this treatment many times over the years on several different things (side panels on my son's Quarter-midget, firewall on my old C-Cab, the dash in my stock car, etc). If you're interested, you can read how I do it here:
http://www.clubhotrod.com/hot-rod-talk/30400-another-build-thread-yep-my-track-style-t-27.html
I also recommend a good clearcoat over the brushed aluminum. It helps the aluminum keep its shine and makes it easier to keep clean.