There is a little soot on the undercoating / thick oil based paint in one picture. Just soot, I wiped it off with my finger.
I noticed that the black paint in a couple of spots under the car on some pieces needed another coat. I pointed this out to him when I was under the car.
Not aware of any rust.
In any case, the mechanic is also a body shop (which is why he was able to handle re-coating the underside, and repainting the underside and inside of engine compartment after removing the engine and all parts, in addition to the mechanical work).
He has done repainting and body work on a couple of my cars in the past. Not concours d'elegance level work, but great work.
For my car he will be doing concours d'elegance level work. He painted a 1950s two-tone Chevrolet in complete Concours d'Elegance level work for one of the actors in the Fast and the Furious series some years ago, which included a lot of chrome replacement.
From what I understand, it's not just about whether the chrome is okay now - which most of it is, some of it isn't - he says that after removing it for the paint job, it will become evident whether it needs to be replaced. Same with for example the trim, such as around the window - the chrome looks fine, but the trim underneath has to be replaced. After all of it is removed, we hope the chrome will be fine and able to be reinstalled - if not, some must be replaced.
He will also supervise all of the upholstery / carpet / interior work and the car will not leave his shop, that way he remains responsible for everything.
I still haven't decided whether to install an original Becker radio and speakers or just pull all of that and install a "280 SL" plate and no radio at all. I suppose at this point might as well spend the money and install all original.