So it continues... I just can't leave this one to the laws of gravity.
I did not find M3 or M3.5 Inbus (Allen head) in the local hardware shops, so ...
Found these 3mm x 10mm screws. They are 2,1mm between the threads, so picked a 2.4mm drill bit.
Used my cordless drill turning it slowly so no metal chips end on the ball screws of the slide.
Since the slide is 40mm wide and the aluminum extrusions are too, I just used a couple of clamps to hold it in place.
Try to drill in the center to be able to have a 0.3~0.5 mm play for adjustments.
I placed it on the flat marble plate and tightened the screws.
Wiring is next and I feel a video coming up in the next couple of weeks.