I have an ST4000+ on an E29. The quadrant is at an angle to the floor. I used a piece of Aluminum bar bent at 90-degrees to start, so that the vertical side could be mounted (at first, temporarily with a clamp) next to quadrant on the wall inside the quadrant compartment, and the sensor could be mounted on the horizontal shelf. Next, I bent the shelf upward to match the angle of the QUADRANT (not sensor, as I previously posted), and finally, repositioned the aluminum bracket so the whole assembly was in the right postion not to interfere with the movement of the quadrant, the sensor was in the right position relative to the quadrant (including the pin mounted to the quadrant receiving the sensor rod) and the connecting rod was in an ideal position to be shortened or lenghthened to tweak the sensor arm's angle to the quadrant. To mount the rod to the Quadrant using the pin, I used two aluminum bars cut so one would fit snugly inside the quadrant sides, and the other would be underneath the quadrant, then the two bars were fastened together with #10 machine screws (this allowed for a low-profile design which did not require me to drill into the quadrant itself). Finally, the pin which receives the sensor rod was mounted to these plates, again with #10's. Trick is to get this quadrant bracket in the right position relative to the end of the sensor arm.
Works perfectly, and relatively simple design. Hope this helps.