Originally Posted by cbdo

103.983 is the type number of the motor in Mercedes-Benz series of engines. It's a designator only and has no direct relationship to the displacement, horsepower, or anything else, except that there are other motors slightly different in the same (103) series. Think of it as a name.

The size of your engine is 180.8 Cubic Inches Displacement, commonly abbreviated as CID. That's equivalent to 2962 cc, a bit less than 3 liters, which is where the "300" of 300E comes from. It's not a reference number but a measurement, describing the total volume available for combustion in the engine.