I have built a larger 300mm cube Hypercube, and after delaying for a little while I upgraded to four 12mm smooth rods for the z-axis. Other 12mm rod mounts were causing clashing between the bearing mounts and my heated bed, so I redesigned some mounts such that the smooth rods are as close to the frame as I could get. As a bonus I can access a few more centimeters of my build platform that were blocked by the z-axis smooth rods.
I have also included a Z-axis endstop switch mount I created that should be a direct switch out from Tech2C's original, but for 12mm smooth rods.
All hardware for original parts should fit with these to attach to 2020 extrusion. To clamp the smooth rod an M3x20 screw should fit. The nut trap might be a tight fit, but you can heat press the nut in place if it's giving trouble.
Pictured parts are printed with coarse layer settings with a 0.6mm nozzle.