Hi, thks for your comment. I thought about the waist mod in the beginning. However, when I play with my small revolttech VF 1S, I found the joint is not that helpful in improving the posing. In considering the operation is comparably big and the stability, I abandon the operation. May be I will build it on the next kit.
Recently I bought some 1:72 Bandai VF 1J kits @ ~US $3 during a local mega sale. This old and cheap stuff contain all the thigh joint and waist joint in the original design. Really amazing.