After almost 2 weeks of doing this process, finally I have done it and I am pretty satisfied with the outcome. I had fun playing around with the articulation but I am kinda hesitant of moving them all the way because of the material they used in the inner frames (which I have mentioned in the WIP Part 5).
I also liked the way the Buster Rifle looks without the yellow parts. I looks nice with the hollowed part in the middle of the barrel. The hand manipulator for the Buster Rifle holds it tight and nicely which perfectly carrying and supports the heaviness of the Rifle itself. I haven't yet tested the Twin Buster Rifle on hand whether the arm can still handle the weight of it when combined.
I haven't yet assembled the Action Base that comes with this kit. I will try to play around using my extra Action Base 1 that I also used in my Tallgeese. Here are some pictures I took in different angles of the finished inner frames: