Your nervous because if something goes wrong, it can be expensive to repair in most cases.
I wonder why it has a new rear end and drive shaft? That seems odd. Is there a history behind that?
Also, with that many miles, the timing chain and upper guide rails should be changed, usually at 100k miles. A mechanic can check for chain stretch and condition of the plastic guide rails. Make sure they're not brittle and yellow in color.
Although, I have heard and read of 560's with well over 100k with the engine never being opened. It depends on how often the previous owners changed the oil. Luckily the 560 is double row timing-chain and not single like the 420.
Sometimes you will hear the chain rattle when first starting it up cold in the morning. This noise is the chain slapping the rails on the left head because the chain is stretched and the tensioner is already at the end of its travel.
If the chain is streched enough, it could snap the rail in half and the piece follows the chain up and gets in between the chain and the cam gear. Then the chain jumps off the teeth of the gear, the cam gets out of time, THEN.....you just bent four exhaust valves on the left head.
I would have a MB mechanic check the car over and run a CARFAX for good measure. Also, HVAC repair can expensive so make sure overthing is in excellent working order.