These steps involve preparation of 3 tailcone "frames" (hoops) that define the size and shape of the fuselage at three locations. The nine tailcone panels are fixed to these.
The frames are in left and right pairs and need to be riveted together. The smallest frame is located where the front spar of the tail is attached, so needs some additional attachment hardware. Pictures 1 and 3 relate to this frame. The "angle" needs to be stdget at the ends to match the curvature of the fuselage skins, hence the two "flutes".
Picture 2 shows a Wear Plate on the bottom of the largest of the three frames. I guess control cables pass over the nylon plate. Over time it will wear, and the design provides for the plate to be de-riveted and rotated through 180 degrees.
