Originally Posted by pawoSD

All of the trannys from the W126 cars are similar, they just have slight variations for whether the engine is diesel or not, and a couple updates to how they shift over the 10 years of production. (later trannys smoothed out the 1-2 shift)

A tranny from a 380SE would bolt up to a 603 (SDL) engine, but the shift points would be wrong for the diesel. The 380 gasser rev's higher per gear than the diesel can, so its adjusted accordingly (different valve body setup) The gasser one on the diesel might work....but it might hold the gears too long when flooring it/under heavy acceleration. A diesel one on a gasser wouldn't work too well, as it'd always shift a couple thousand rpm below what the gasser was capable of and thus could lug the engine.