Bryan Cotton wrote:Anthony,
I don't have the plans in front of me so I can't give references. If you look ahead you will see there is a big aluminum Y that mounts to the tailpost, and this is riveted to the aft spar on final assembly. The flush rivets let the Y lay flush on the spar. The Y does not go the full span.
I also don't have plans in front of me but what Bryan says sounds correct. The inboard ribs are attached to the rear spar channel with countersunk rivets to clear the "Y" tailpost, but the outboard ribs don't have this conflict and use CCP rivets.
You can test this by just laying the larger "Y" in your kit against the back of your substructure to see how it fits.