Madd, just finished doing this to the factory manifolds on my 400M. I almost forgot about this trick and it works excellent on cast iron or steel, it actually lasts longer on rusty cast iron...seems to soak into the rust and stay put. It is water based so there is no smell when you first start it up too.
“She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself.”
— Han Solo