There was only one scene in the film where the arm was ever fitted up as a whole piece with the central mechanism built in for real and not digital.. which was the scene when it was hanging on the truck. Which was one of the first scenes we ever shot.
I can send you a photo of the whole rig as it was on the truck with the central forearm shaft which is what I imagine you will want to make. Charlize could only physically wear most of it and have the finishing touches of no actual arm - digitally added
[. . .]
As seen in the gif from my website the central mechanism is different in the rest of the movie where it has been altered digitally instead of the real version .. so which version you make is up to you..
George Miller the director was never a huge believer in continuity...