Here are some pretty unique photos of the E46 M3 GTR race car I have personally taken at the Munich BMW Museum.
The Museum staff were very kind to open the car for me to take photos of the interior and the engine bay.
I had to crawl under to take the suspension photos.
The photos are my copyright and not to be re-used without my permission.

The setup of this E46 M3 GTR is of the Nurburgring 24 hour race.
You can tell this by the rear suspension setup which is similar design to the road E46 M3 (3 links).
The most exotic setup is of the ALMS M3 GTRs which have similar setup to the E36 320i STW (multiple links with push rods).
If I am not mistaken, that setup was designed by McLaren.
 

Here you can see how the rear suspension of a 320i STW looks like.
Photos of another photographer.