Degrease it before you sand,You don't want to sand any contaminates into the paint!! You can feather out all the bare metal or scratches out with 400 wet-dry paper and water-wire brush any rust(on a drill) then take a scotch brite pad and some comet or ajax and wash the hole thing GOOD!!! wash again with soap and let dry.Put a lite coat of etching primer on the bare metal spots, let it flash(dry to touch) and then paint the hole thing. pj-1 works fine for what you are doing! Other than that ,the best way is to sandblast the intire frame and start from scratch!! Tape any oringinal sticker off,and protect them(it makes the job look best!!)