Here I was getting ready to make the shims that go between the rib trailing edge and rear spar. The Rear spar is really the bottom skin curled up. Any way, in image 1 you can see I'm pointing to a small gap between the rib and skin. Image 2 shows the gap closed by just pressing down on it. This gap must be removed before you dill the rib trailing edge through the rear spar.
You need to match drill a hole and insert a cleco to close the gap. Interesting the hole exists on the skin very close to the trailing edge but not on the rib. So, just match drill through the skin and cleco to close the gap. Now your ready to insert shims and drill the trailing edge through the rear spar.
Man, takes longer to write about then it does to do it.