For the aluminum frame, you may be stuck with Birchwood "aluminum black," or else some kind of paint. Aluminum-black will improve things a bit, but it will depend on how badly the finish is torn up. And it's not particularly durable.
If you go with rust blue for the steel parts and aluminum black for the frame, I suspect you'll have something that looks quite nice, and it will be a fun little project that requires almost no specialized equipment.
If the frame is very badly beaten up, so that aluminum-black just won't cut it, one possibility is to spray the frame with brownell's aluma-hyde. It's another paint and presumably not as durable as cerakote, but one can is about $25, and I guess you can always touch it up.