Spray oven cleaner (~5 min) will eat thru grease and remove anodizing leaving bare Al metal. Leave it on ~10min, to leave behind rough "paintable" surface. Chemist speak - Use oven cleaner containing NaOH (Sodium Hydroxide) It dissolves Al. I've used this on small aluminum parts on firearms. It should work...

Be careful, NaOH is NASTY.

Then again, sandblasting or beadblasting might look better.

<<Well I go to college in Daytona Beach, FL and I found this guy in the phone book who did "polishing" so I gave him a call. He told me he did valve covers so I took a ride and went to his place. On the phone he told me about $25. When I got there and showed him my valve cover he said. "Holy shit that's a big valve cover!". So I thought it was gonna be about $50. He wound up doing it for $25 though because he said that's what he quoted me so he turned out to be pretty cool. He did mostly all Harley-Davidson stuff for bikes but also did wheels and anything that could be polished! Took him about 4 hours to do. Came out pretty nice.>>

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