I have Rover standard cast iron manifolds on my Plus8. A small amount of surface rust. I cleaned them with a scotchpad soaked with Pepsi. The acid in the Pepsi was tried to help cleaning and convert the rust. Worked fairly well.
It might also work on steel but probably not on stainless.
A couple of weeks ago I re-did them but tried brushing on some Kurust. They went a nice dark/black colour and I am watching to see how long for.
