I have built a quad setup based off of your build with slight modifications
I didn't take any pictures during as I was too excited to get up & running
So here are some shots after (don't mind the messy desk). In my setup its actually 3 separate computers. I used black iron mostly because where I grew up (Galveston TX) it is illegal to use so I had never seen it before and thought it looked neat
I tried with 45's but the angle was too great, so my thoughts are:
A) see if I can either locate some 22.5's
B) just bend the conduit clamps slightly
C) something adjustable between the conduit clamp & faceplate
Did you ever resolve the monitor rolling issue? As you can see i put wing nuts on mine but that acer in the top right is heavy and wants to find its own resting place.