Finally I managed to assemble the rig (not easy when doing it for the first time and maybe I did something wrong), but my Sapphire Radeon R9 380 GPUs seem to be too short for laying on the "back" beam.
So they can only being held by the screws on the front beam, I am not really happy with that. Or did I assemble something wrong (so an answer to my question above would be appreciated)?
Kind regards
The GPU support beam posts can be fastened to the *side* of the middle motherboard beam, as shown in this pic: