I worked on Fusion 360 for around 4 hours and I think I've got the arm designed for a 3D Printing test. I might play with it and refine it a little more. Eventually I would like to print this (if it works) out of Nylon/Carbon filament.

Front view, I still have to put in the shock and pivot holes.

This is the outside of the arm. I'm going to try to put the notch in it for the rear carrier.

The inside of the arm. I made a relief for the out-drive, it should clear.