Yes, the chain would jump ahead of the cam if it slipped and the cam would be retarded which would have been improved with a new chain even if in the wrong link.
idle roughness is either a symtematic lean condition or a specific one on a 560 in closed loop. Try running the engine with the air cleaner off and slightly depress the air flap. If it instantaneously improves the idle the above conditions are proven.
To tell whether it a systematic of single cylinder problem open the lines from the fuel dist to the injectors one at a time sopping up the small amount of freed gas and watching how the engine runs. A distinct misfire will occur on good running cylinders. Poor running cylinders won't make much difference.
If they are all the same and the engine responds to the air plate deflection then you must see if the engine is running in closed loop before proceeding.
Bosch Master, ASE Master, L1
33 years MB technician