Help - What part is this on my CB650 Nighthawk?

I recently bought an old 83' CB650 Nighthawk as my first bike, and I've been kind of learning a ton to start working on it, but one thing I haven't been able to figure out is what part this is. Is it a stock part, or is it a mod that the previous owner (who had been working on it for a while) did?https://i.redd.it/60onw6r11vh11.pngAlso, there's some rust on the frame as you can see in the left of the image, what's the best way to deal with that without completely stripping the bike and taking the frame to a powder coating place?Thanks!PS: This weekend I'm swapping out the carbs and replacing the engine value cover gasket. Fun! via /r/CafeRacers https://www.reddit.com/r/CafeRacers/comments/99o9h2/help_what_part_is_this_on_my_cb650_nighthawk/?utm_source=ifttt