Picture 1 - these gussets are riveted to the "step" bulkhead side channel. There are holes in the top to rivet to the longerons, but there are no corresponding holes in the longerons at this stage, and reading ahead I have not seen any step in the plans to match drill these into the longerons. Note the picture is confusing. The longeron is not attached properly yet, and should sit on top of this gusset.
