Marked center ribs (left and right) with the 110 mm and 85 mm distances for the center channel L brackets. Drilled and cleco'd two #40 holes through L's and ribs along the line. marked the overhanging portions of the L brackets, then removed from ribs and trimmed off the excess and smoothed with a file. Reinstalled to ribs.

Marked a 10 mm line in from both ends of the center channel and drilled two #40 pilot holes in each end. Clamped the channel to the L brackets and made sure everything was flat and true on the bench, then drilled and cleco'd #40 through the channel and into the L's. Drew the centerlines along the rib flanges and the channel flanges and on the remaining four ribs. Stopped for the night.