Since I have the newer nylon knuckles, the original design didn't keep them from shifting and throwing the calibration off, so I simply cut off the unused holes and added posts to keep them securely in place.
I used ProtoPasta Carbon Fiber. It's PLA so it'll be interesting if it holds up and doesn't deform. Definitely light, but given the properties of PLA it could still warp if it's too warm. While I marked no supports, you can put a couple custom placed supports under each post if your software allows it. I used Simplify3D and placed some supports, it was quicker than removing all the internal supports the software wanted to place.
Ummm... eh... not really. It wasn't until I retired the effector in favor of 713Maker I realized I was performing some level of calibration way more often than I needed to. The peek fan would blow hot air onto one side of the effector which you can see in the pictures below visibly warped it. Mind you this is hundreds of hours of print time on the effector. If I was to print this again with carbon fiber in mind, I would opt for XT-CF20 or anything other than PLA (i.e. ABS, PETG).