Just finished putting this back together today. I received it a few weeks ago and it had two different colors of paint on it, so I let the various pieces of the case soak in a electrolysis bath for several days and then primered it and painted it. The grate was treated with phosphoric acid, iron burner was heated with mapp gas torch and coated with mineral oil, new check valve and new nitrile gaskets and it runs very well. The iron burner is stamped "6337", so I assume it was made in 1937, which makes this a 6F. The 6B was made in I believe 1931, but appears to be almost the same as the 6F. I left the fuel tank in its original state because of the painted on coleman logo.