Fabricated and installed piano hinge on seat pans per plan. The details for this are on print 29 and there are about a hundred different dimensions called out for everything from where to trim eyelets, to the hole pattern. Lateral position of these isn't super critical, but fore & aft placement needs to be pretty precise. The furthest aft one picks up a couple of holes that are common to the floor ribs. Just a little too far forward or back and you would run into edge distance problems on the hinge at those holes. Also match drilled for nut plates common to the center tunnel ribs. Previously I've used oops rivets for nut plates, but this center tunnel seems like it's kind of a big deal structurally, so I like the idea of that being as strong a joint as possible, so just like in the baggage area, I dimpled everything and will dimple the ears of the nut plates that go on the back side of the stackup.