The STEP file should make seeing these surfaces and making your own changes easier.
Definitely print in PETG since you need that sticky, but slightly bendy, properties to make sure nothing snaps like PLA. Though, you'll probably have no issues with PLA. ABS/ASA is overkill and stinky. If you're feeling bold, print in PC but good luck.
The box was designed by me, but I haven't uploaded the model :P . If you know 3D modeling, than the Neutrik website, coffee, and an hour should get you 90% of the way there.
The author remixed this model.
Tighter Tolerances for the keystone itself. This made it WAY more reliable when I installed 6 of them in a stage box. Previously, the variance between keystones meant that if you push at an angle, the port pops out. No good.