The first step in working with any ribs is to flute the flanges so that the rib lays flat. It took me a long time to do this for the tail feathers, but I was amazed at how fast the process went this time. Something ‘clicked’ in my hand/muscle/insight system and I was able to flute these ribs with just 4 - 6 gentle motions which all had a visible effect. This photo shoes a fluted rib in the foreground and an untouched one in the background. Note the background rib is visibly bowed up and you can see a sliver of light under the middle lightening hole. The foreground rib is laying flat after only a few flutes.
Here’s the entire collection; some with nose flanges removed, some with rear flanges removed, some with none removed, and others with intact nose flanges but removed rear flanges. The removed nose flanges will (probably) be where the stub spars attach. The varying lengths of the rear flanges are probably due to the stepped nature of the spars with the thickest parts of the spars being closer to midline of the aircraft.
These have doubler plates and/or K1000-8 nut plates for the electrical connections and the stall warning vane, respectively.