If you're getting frustrated then take a step back and take a break. This is supposed to be fun. In the pictures above everything looks fine in terms of placement. I see what you are saying about the way the kidney piece is angled and keeps you from placing a straight shim between it and the ab plate. I would get some of the scrap ABS you have and make shim, and tape it to the ab and the kidney so that both pieces sit straight up. If that means that there is a tiny space between your lower back and the kidney plate then so bet it. I think that is better than having an angled or triangular shim showing on the side of the suit. How are you hanging the thighs? Are you using a garter belt system? This is something easy to make if you need a break, but I think you need to have the main body assembly done first so you know where (height-wise) to hang the thighs. Get out the tape and put some shims in place and see how it looks. Keep asking questions and we will get you there