I have made one for the E34/M30 and per OEM real the pans are the same. So this should fit your M5.
I have been making skid plates for the E30 BMW for years now. After picking up my own E34 I see the need for one here also. This is what I have made for my self. I will make a short run maybe 5 or 6 to test the waters. If you want one let me know. They are made of 10 gage steel, laser cut and come with all hardware and instructions needed. price is $185 shipping will run $15 to $30 from Vancouver WA. please feel free to ask any questions you may have.