Thanks everyone. @theiceman I did use the Autosol. I combined that with 000 steel wool. For the more difficult areas I found that a Dremel with brass brush worked the best. I even did some wet sanding with a variety of high grit 600-3000 just to see what would work best. The shape of the blades etc. make is a challenge to use electric tools in a lot of areas so a lot of hand work was necessary. Once I started to fit the fan back in I realized how bad the shroud now looked so I did a quicker job on the visible areas to dress up the whole thing. Thanks for the advice.

 

yup that's EXACTLY how i did it , brass brush on the Dremel , steel wool and Autosol.. nice results ..