Yes, you can use the SliderPLUS v5 and HeadPLUS v2 setup while mounted upside down.
At this time, we do not have a rig that can be used to mount the SliderPLUS and HeadPLUS upside down, so please be very careful when building one!
If you have any questions, please contact our Customer Service team at support@edelkrone.com. We are happy to help!