Thanks for the tips. Actually the rust problem is as much on the inside as the outside. This suburbans story is that the engine was rebuilt by a shop in Portland in 1975 (I have the receipt). The engine was then put back in the truck but the fuel pump and a few other things were not reinstalled and it sat that way for 30 years. I pulled the engine and removed the pan to find a gigantic mouse nest filling the oil sump.The moisture from the mice caused a lot of rust on all surfaces that were not oil coated by the rebuilder. I have been carefully working at it with a wire brush but its kind of a slow process since I have to be careful not to mess up the machined surfaces. Thought there might be something I could apply with a brush that would remove it.