If your set on your paint route I see no problem with using ospho (phosphoric acid)as your metal prep.
I'd hit it with 80 grit after the wire wheel then ospho before your Rustoleum primer.
Like I said it took sand blasting to remove the tar on the inside of my fenders, I wasn't about to use up to 1/2 a gal of reducer on it... But it was sure free of rust and nice looking metal!
