He mentioned it clearing the fuel tank, and then the back up light was the give away.
You did a great job installing the system. How did you bend the pipe? Do you have one of those HF pipe benders?
The stock MB Mufflers are a straight through design. What kind of mufflers did you use? I copied the following from another MB Forum.
The stock mufflers are a straight-through, unbaffled, design and the diameter is already large even compared to modern cars.

Charlie