Update: 11/21/2018: I ran into some PTFE that wouldn't fit into the guide arms, it was thicker than what I was using before, so I have added two arms that are slightly larger diameter to allow for this.
Update: 11/15/2018: So I have moved on from the awesome universal spool with the screw in sides. It was just a bit much especially when I needed to change out a filament. So I designed my own hanging spool (inspired by many others available on Thingiverse). Anyhow, the hanging spool has a clip that goes on the top part and it is secured by a short M3 screw that is used as a set screw. Retraction arms and levers are still pretty much the same but I added a slight bend inside the large lever (guide) to create a little fiction for the filament as it goes through the PTFE tube. I found that with full spools the filament would sometimes push back through, but this is no longer an issue with the new lever/arm.
For the latest setup you need.
You no longer need bracket.stl and hooks unless you still want to use the other spool holder.
To manage retracted filament from the MMU. I wanted to adapt the thing by TheZeroBeast to work with the universal spool holder that I have been using for some time, since the concept seemed to work well with the spool boxes. I ended up remodeling everything in fusion as I needed to change some of the parameters to work with the space available. After some trial and error this is what I have now and it seems to work well enough.
You will need some of these.
Fusion 360: https://a360.co/2Qz9wcr
No supports when oriented correctly.