Drilled the right wing leading edge upper surface to 40 then began drilling to 30. I didn't follow the manual on the sequence. I drilled the spar first then one hole in each rib working forward. I used two 2x4 weighted with 50lbs of sand bags to hold the skins to the ribs. Drilled one row then adjusted the boards then drilled another row. when I got to the last two holes the boards were removed. I couldn't have done this without help. I would move the rib and Carlene would tell me when it was alinged. She would hold the the rib in place using pressure and I would drill and cleco. After a couple of holes were drilled the ribs stayed in place.