WA 49-38,
I put a braided wire drill brush on my drill and went to town on the engine end of the frame. It worked great for knocking off all of that crud. If you hit the rusty spots with a clean braided bit, it will clean that too.
As far as Zero rust, I have never used it..
I will admit that I have used (Gasp), Rust-o-leum Rusty metal primer...I figure it is cheap and works well. Since I plan on taking my truck down to the frame someday, I don't want to spend the $$ on other more expensive rust stuff.
Since I live in a road salt state, I do know that RustOleum Rusty metal primer along with flat black rust-oleum paint I put on in 1983 is still on the bottom of my dad's steel snowmobile trailer.
