If its the newer prepunch kit, all the rivets that hold the rear spar on are done last. IIRC, you rivet the nose rib into the skin first, then the HS framework, then last the rear spar. The innner and outer ribs face outward so you can squeeze them, the rib in the center gets pop rivets. I believe its the last or second to last check list item in the written instruction under "riveting the HS"