Propane is widely used in the light trucks for extra performance. In a 5.9L Cummins engine up to 125 HP can be gained, but the strength of the rods and crank are in a league of their own. I would suspect that 25-40 HP would be more in the range for the MB diesels. Done right it is safe and will not harm the engine. Done wrong and it can be extremely destructive. If too much propane is inducted it can ignite on its own in a high compression diesel, and is called detonation. Detonation will lift the head, the diesel is injected into a hot flame and combustion control is lost. The timing and duration of burn are critical for a diesel to operate. Propane can also ignite in the air induction system if a valve is partially open or there is a corbon hot spot etc, and when it does the result to the turbo is usually catastrophic failure.

Some quick points.
Propane is injected into the air induction system, not into the cylinders.
Combustion temps rise little if any with moderate charges.
Fuel economy is improved quite a bit, but how much depends on when and how much is used.
Tanks must be DOT certified, and are more reasonable than you might think, around $200 to start.
Smoke and particulate emissions are reduced.
Power and throttle response are dramatically improved.
It will not help starting, it is only used in high power situations.

The number one thing you guys should know about propane is that it is used on an as needed basis, not continuously. Most systems are boost triggered ensuring that the propane is only injected when conditions warrant and are correct for its use. A Hobbs type switch is used to trigger the propane solenoid, and a regulator determines the injection quantity.

It would make tight freeway ramps much less interesting, and the response of the engine would be much better in all high power situations.

I would think a charge air cooler would be safer and easier on a MB with cost being the about the same. The market of MB owners willing to use propane would be small in my estimation, so you would be developing the system for yourself with assistance from the component supplier if you decided to do it. Developing the system is not for someone that is not capable of making any repair necessary, monitarily or physically.

Hope this helps.