Below is a photo of the OEM rear valance trimmed to fit the Eisenmann quad system:
I have a few more detailed photos of the trimmed OEM rear valance that I would be more than happy to send to you. That way you can bring it to the shop and give them an idea of how the trimming has been performed in the past. The trimming of the valance should take the shop no more than 2 hours.
Alternatively we have sold a few 3d Design carbon rear diffusers and the quality and fitment is excellent. A couple pictures of the 3d Design product below:
