Lurked for years, thought I had an account, discovered I didn't, now here I am. Figured I'd make my first post a good one.
I recently.....obtained.....this '75 'one owner' W115. It's a lot like a baby first thing in the morning; looks nice in the front but the bottom is
nasty. This isnt a post about whether or not its worth saving, as I intend to put my best foot forward and give this old car another chance, this is more so about documenting my process, gathering feedback and expertise and hopefully coming out on the other side of this with a halfway decent vehicle.
Background: Car was purchased new by 'this rich guy' and driven for years until husband and wife died. It was very well cared for with lots of documentation. Son inherited it next and, well... he did his best.

The guy I got it from bought it from the son and a year later, flipped it to me. Here we are.
It's a halfway low mileage car with 127k documented miles on the clock and it runs amazingly well with no blowback or smoke. I haven't been brave enough to try and drive it yet as it has what I believe to be some semi-severe structural issues from rust and a horrid patch job on the pans. It's going to be a little bit before I get started on it as I gather knowledge and parts.
How would you tackle this?