Polycarbonate is a neat building material; it has a lower density than aluminum, but is much more flexible. It has some good applications, but I don't think that replacing aluminum channels in a drivetrain is usually one of them.
Being lighter isn't always the best attribute. Sometimes you need a material that is stiffer rather than lighter.
That said, it's great to see you built the design and tested it, that's worth way more experience than just hearing people on Chief Delphi say "that won't work very well". Kudos for that!
The zip tie bearing retainers are great, I highly approve of that fix.