Finished up spar notches to complete all ribs for 10 ribs per panel.
Used scrap length of carbon tubing to try to create tooling - a long hole saw - brass tubing would have been better but didn't have any handy.
Used surface gauge to mark up the center section box walls for hole locations.
Fabricated 1" end-grain balsa retention block faced with cross-grain pieces, located with spacer blocks and bonded to floor of control distribution center section box.
Fabricated a fixture using some scrap MDF for a base to try to drill the center section box for the four spar tube/pivot locations. Corner blocks locates the center section and holds it firmly for drilling process. The carbon tube had to have teeth filed in after each hole attempt and used a brad point to finish job on each wall. During the drilling process the cutting end would get hot and burn away the resin leaving fuzzy carbon strands. Suspect sharpened or toothed brass tube should have worked much better...
Final pic shows center section with one full length tube running through with the two short ones butting at the center.