I vote for a fuel injected M129/130 engine. The main point of emphasis here is good ol' rock solid mechanical fuel injection. The V8 4.5/3.5, stay away. Not worth getting mired in electrical issues, and some of the bits for that early electronic FI system are very very pricey and difficult to get right. The M130 with fuel injection typically only has one temperamental part: the cold start valve located on the intake manifold. Other than that, it's very straight forward, and is simple to tune and adjust. One of my all time favorite mercedes engines...with the M110 being my least favorite.