The car shows a lot of tell tale signs of being rusty. Of particular interest is where the inner fender on the right at the rear appears to be welded under the undercoat. There is a thread here of someone who dove into exactly what you are facing and it turned on him badly. To his credit he has stuck with it and is doing an admirable job of it.
https://www.sl113.org/forums/index.php?topic=21397.0Here is how to do a quick check of the car:
the factory undercoating is an off white that over time turns to a dark brown almost black color. If the car has the same black tar as under the hood it probably has had floor work. The main areas of rust are the front and rear of the rocker panels (Sills), the frame rail just behind the sill and the trunk floor on the left side. Under the hood there was no undercoating so that was done to cover up work or to tidy up after a color change where the engine bay was the original color and black was a better look. The best gauge I have found is to reach up inside the front wheel well on the inner side there is a rectangular section sheet metal channel running fore and aft. Reach up to the top and feel for rust holes. This spot is easy to miss and if it is rotten there it is probably rotten everywhere.
As far as mechanicals if it turns over it is probably worth getting running. The fuel system is your biggest hurdle but if you have a decent mechanic the people here can talk you through that. DO NOT HOOK A BATTERY UP AND TRY TO JUST CRANK IT OVER WITHOUT VERIFYING THAT THE ELECTRICAL FUEL PUMP UNDER THE CAR IS RUNNING. If it is stuck it will burn up and new ones are $1600. If the spare tire is on a post on the right side of the trunk and not vertical new fuel tanks are available from a company called Dansk for about $400. I suggest buying one as the inside of the tank is fairly complex and hard to get properly clean. There is a pretty good chance the injection pump will be gummed up but is can be unstuck usually on the car.
You can get a copy of the Data Card which lists colors, engine number etc from the Mercedes Classic center. The instructions are in our Technical manual section.
Having flipped more than a few cars in my youth I would get it running( if it isn't stuck) and send it on it's way.
Here is the rail in the fender well.