.../... the engine has been replaced with a 280SE/NV .../...Can anyone tell me what the background of this engine type
The engine type is indicated by the number after "130" on the engine ID plate and/or punched into the engine block. In your case perhaps 130.981 or 130.984(?)
Compression on such a low compression M130 NV is 8 to 10 kg/cm2 at running temp; minimum is 6,5 kg/cm2. Nominal compression is 7,8:1.
A normal M130.983 engine as mounted in a 280SL /8 Pagoda has 10-12 kg/cm2 at running temp; min is 8,5 kg/cm2. Nominal compression is 9,5:1.
A lower compression engine can be run on lower grade fuel