Since I loved the Reprack system, I've designed a reprack-alike system for top down mounting. Since the distance between the rods is the same as in the original Reprack system, other accessoires are compatible.
I used M5x20 bolts for the connection between the two parts.
Just slide the 2 Ikea Räcka in and you're ready.
I used ABS for printing, but other materials will also work.