the W140 (this shape S-class) was never offered with the M112 V6 or any other V6 for that matter. th eonly 6 cyls it campe with was the M104 which was inline (engine in pic is a V), only the M109 and M113 V8's were available in this car.
also the engine cover is distinctly that of a V8.
seems the car has been facelifted (side panels, bumpers, grille, indicators, rims etc), but the work has been done VERY well and the car looks exquisite. congratulate your friend for me, it's great having 321 hp on command in the W140.