I bought a set of these fine wire brush tips for my Dremel tool and went to work. It worked great. Use the cup and pen shape for between the fins and around the head bolts and the wheel shaped ones for the big flat areas. Use medium speed on the Dremel tool, take your time, and expect to go through several tips. Make sure to wear glasses you don't want one of those fine steel bristles in your eye.
https://www.amazon.com/Drill-Warehou...GYAWF638FX7B4X