Thanks for sharing those nice pictures!
I had experience myself with citric acid (a very good alternative to evapo-rust) for some Macintosh cases. It works like wonder. But this is chromed? surfaces, most of the rust is not exposed. On those yellow-looking macintosh frames, the lemon juice removed the "yellow" coating as well, leaving bare metal which would rust by just rinse it. As you said, I did use galvanising spray afterwards, the result was brilliant. For a case like yours, it's my favourite process too.
Here is my process with the Macintosh: https://youtu.be/crMj03OQlhQ
But this frame is almost glossy so I'd like something similar to replace the coating with.
Now, the PS/2 floppy had some similar corrosion inside and I sanded it with a wire wheel. What I found was that there was no "coating" coming off. I'm not sure what the process was but in the end I just applied a thin layer of oil and happy days - though you can still see where the metal was eaten away from the rust.
I think I'll start with some scrubbing and rust removal. If that works, happy days. If not, I'll prime and re-paint.
Thanks for now!