If I came across a good deal on a W140 rodbender, I'd just locate another known good OM603.96 and drop that straight in. SDL donors can be had for fairly cheap these days. The only caveat would be the frightening level of electronics found on the rest of the car--very complicated.

I think an OM617 would have to struggle mightily to move that big hunk of steel around, and would no doubt return lousy fuel mileage.