I just built a set of wings for a Bridi Killer Chaos. It also has the slots you speak of. I have heard of people using music wire in the slots as a jig. However, I followed Bridi's instructions and drew a line on each rib front to back using the slots as reference to the centerline of the rib. When building the wing, pin the top (most likely) spar to the plans, put the ribs in place on the spar (do not glue yet) and block the rear of each rib (you have to cut your own blocks) with a wood block. slide the blocks for and aft until each rib center line is parallel to the building surface. I tacked each block in place with a small drop of ca where it touches the rib. Next, I believe I glued the trailing edge in place, making sure that all ribs were perpendicular and parallel to the surface. This is a start, If you have any questions feel free to email me.

Ed H