I measured out the positions for where ribs 1-4 should be on the front channel, then drilled where the holes should be in the channel first. NOTE: the top and bottom holes would not meet edge spacing requirements on the rib flange if I had drilled them as per the plans, so I adjusted them slightly. I just lined up the holes with the center lines and attached everything. For the "L" angle at rib #5 I attached it to the front channel first, then to the rib.
