Hey, this was one of the parts that stumped me on my build but I found a pretty good solution. I did just what you said. I 3D printed them and traced them onto paper. I ditched the 3d printed stomach piece and I completely free handed EVA foam a piece that stretched from my stomach, to my upper chest so all of the torso pieces could connect as well as those new foam shoulder straps. that I glued onto the back. Ive seen some people layer foam around the decorative nylon/elastic straps too and it looks really good, I have also seen them wrap them in fabric which looks great as well. I was running out of time and just plastidipped and painted mine, threw elastc and nylon on, and found some decorative buckles. I was a bit iffy with how it would look but I think after the weathering it was good enough for me! I also chopped off the bottom undersuit pieces on the back piece cause they were jabbing me, I dont have pics but I re-bondoed them and painted over them. For the small side plates of the lower torso, I put heavy duty velcro on them to connect the foam vest piece to the back. Hope this helps because it was a bit daunting of an obstacle for my build! I can take some more photos soon of the whole thing all cleaned up as well if you'd like!