If you have an original,unrestored bike that is in incredible shape, it can be worth more if it’s left alone ,as long as you can get an original cylinder head.
So this begs the question as to what you intend for the bike, or what is important to you. Once you paint the frame, it is no longer unrestored. If you paint the frame which will now look brand new, will the other parts also need to be “ restored “. So, is the frame and swing arm that bad? If you can’t get an original cylinder head or have to paint the cylinder head, then you’ll need to paint the rest of the motor...so....then you might as well go ahead and paint the frame. Once again, it’s all in what you want.
To answer your paint question, you’ll get various answers as to the correct shade of black. Some will say satin black, or semi- gloss, or even gloss black. And of course, powder coating in place of spray painting.
I’m not a restorer, but I have an original,unrestored 1975 550 f that is mint. I have done extensive research on these 550’s ,including paint. The closest black color I have seen is a product called “ under hood black” by Eastwood Co. Just another option you can check out. Your choice.
I’d like to see a pic of your bike, you should post it.