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With the wing square, I fit the forward rib first. To have access to the pilot holes I have to remove the neighboring ribs and use a flexible shaft attached to my drill.

      After the forward rib it is on to the rear root rib.  After careful fitting it is clamped in place and then all the pilot holes are drilled at both the fore and aft attach angles.  Like the forward rib, the neighboring aft ribs need to be removed for access.