While your arm design does seem fairly accurate, the way they connectors are attached that allow for the shadow trap as shoulder armour seem like they are a bit problem filled;
Problems that occur from this design include the rod piece not connecting fully, the rib piece being bent outwards and not connecting properly to the balljoint, general flimsiness with the connection and potentially bending pieces to ensure they are lined up.
I’ve built a rough version of the arm to test if these issues can be fixed with the current design the way it is, and it is not possible in my view. As such, I’m going to vary slightly from the official design when it comes to doing the upper arms on my version, as i feel the proper design for the upper arm has a high potential to cause issues.