To locate the outboard seat rib I first trimmed off about 1/8 inch in the forward end because this amount rode up on the radius of the bulkhead web.
I drew a centerline on the bottom flange.
I fluted the rib to mathc the curve made by the holes on the bottom skin.
1) I match drilled the rib to the bulkhead. I noticed slight up & down space so I made the rib rest flush on bottom skin.
2) I match drilled the bottom flange to skin. I looked for the center line thru the skin holes and drilled it.
3) I match drilled the top rib flange to floor skin leaving a .032 space so that the rib web sticks outboard farther than the floor skin. I used a piece of scrap for a spacer gauge.