Tried to use the original that this was remixed from but as I'm using silicone spacers it sat higher than my bed. I also made sure to leave some clearance for the internal spool holder mod that I'm running.

This attaches to the arms for the Z axis rather than the cross bar. 

One of them has a cut-out for the the Heated Bed cables.

I used an M3x16mm screw with a T-Nut for each one.

As it is close to the bed I'd recommend printing in ABS. 

I use a 0.6mm nozzle and printed with a 0.3mm layer height.