Carl,
While looking at the pictures and your description, it seems that this car is a bit much to handle for that price.
Depending on your level of repair work on these cars, this one will require a lot to bring it back to a good tick.
Engine noise-piston slap meaning the lower end is worn, an engine out job. You didnt mention anything about how the car was cared for, what kind of people drive the car, oil changes, maintenance, etc.
Best to have an expert look over the car to determine it's true heritage. Also best to put it up on a lift to look at the undersides. Trunk?-no clue to how it looks(should have the vertical spare tire) Sloppy gearbox means the bushings are worn. Blistering paint on the fenders means the underlying paint has reacted to the top coating of paint and lost it's adhesion-total strip to bare metal required to fix. Rust issues-obviously the owner has something to hide. Look for the jack points and try the original jack to lift the car. If you hear any crunching or groaning of metal when lifting the car with the jack, stop and let it down again-metal is rusted through behind the rocker covers.
Also if you cant get the car onto a lift then I would simply lay down on some cardboard sheet just before the rear wheels and reach under the floor in front of the rear wheels and feel the chassis frame just before it swings upward over the axle-should be smooth with the undercoating, if it's rough or has jagged edges or a hole then it's rusted through.
Just a few pointers that should help you determine the buy or not. Do not go with your emotions for the purchase. Walk away and come back later when you have thought it out.
There are plenty of others out there to pick from, just takes time.
Happy Holidays to all!
Walter Klatt
1967 220SL-diesel
1963 230SL-gas