For the past 25 years I have used products made by a company called Bill Hirsch, I have used their manifold paint on my 66, my manifolds are cast iron and his product makes them look clean and new without making them look like they have been treated. The paint lasts and lasts. A bit pricy but I would use and recommend their products. I'm sure if you called them or email them they can advise you what product to use for the finish you are looking for. Here is their web address for the manifold paint and from there you can get to their homepage. Hope this helps.
http://www.hirschauto.com/acb/showde..._ID=11&CATID=1
This is the URL for their rust remover
http://www.hirschauto.com/acb/showde..._ID=16&CATID=2