In the end I found a motheboard and I think I am going to try the building of the system...
Do you know @Venturi if the space between GPU slots are standard spacing (4 centimeters)?¿?
I have attached two pictures to this post:
One shows distances between the holes of the board
The other one is the tray I have to fix the board. That tray has 11 slots for cards...
With the one that have the distances and looking at my tray it seams that I can fix the board to the tray in at least four holes...
What do you think about that @Venturi
It seems that the holes on that side of the board (gpu) are the standard distance, except for the bottom one in the corner, at least from where I am looking. You may have to post one separately in the corner. At least from my view