The 16 flap ribs have to have a tab trimmed off the trailing edge. I started cutting by hand using my Dremel tool, but I wasn't happy about the result. And, I had 15 more to do. So I built a holder and a fence for the Dremel so I could adjust the cut depth and then accurately slice the tabs off the remaining ribs. The holder and fence were worth the effort and I now have it for future jobs. I also polished the edges, adjusted the flange angles and flattened out some puckering and final drilled and deburred the holes.