I cleaned up a 1979 Honda CX500 that had been in a shed for six years, but it was not as bad as what you have there.

0000 Steel wool and some chrome cleaner did a decent job removing rust from the old Honda's chrome, but some of yours looks like it is not surface rust.
Much of the rust and crud I removed with a brass wire brush. The brass brush doesn't seem to mess thing up quite as bad as a regular steel wire brush.
Steel wool, fine sandpaper, chrome and aluminum cleaner, a paint cleaner and/or rubbing compound and lots or work.
Doing some disassembly will help in getting access to many of the areas.
Waxing the bare aluminum will help with the oxidation, but uncoated aluminum has always been a PIA for me.
You may be able to make it look much better, but it isn't going to look new.
Some painting appears to be needed as well.
If it was anything but a Harley, I wouldn't waste the time on it. Being as it is an 883, it won't be worth a lot when you are done even if it is a Harley.
It might be an interesting project/challenge, but it will probably frustrate you a little.
Just a comment on it being "uncovered". Much of the corrosion would probably have occurred even if it had been covered. The covers seem to trap a lot of moisture and condensation can be really bad under a cover. I have seen engines that looked like they had been sprayed with a hose.
I have an expensive cover that I don't use because of that condensation.