Scotch Brite on a wooden dowel or wooden "paint stirrer", so you don't mark them up with a metal dowel or spoon. That'll get the corrosion off, but will scratch the surface. Once it's scotch brite'd, hit it with some 00 steel wool, then 0000 steel wool on the same wooden dowel/stirrer. If you're going to leave it bare metal, just be prepared to spend a lot of weekend hours repolishing the fins.
...OR, if you know someone in the business, have them bead blast the outside with glass bead shot. It'll give it a "metalcast" or "satin" finish that looks great. I'd suggest hitting the outside with some high quality clear engine enamel if you want that bare metal look.