Removed protective vinyl from and deburred step ribs and bulkhead. Dimpled top holes in top flange of left and right inboard step ribs. Dimpled the six sets of nutplate attach rivet holes in the top flange of the bulkhead. Riveted the step ribs to the bulkhead. Dimpled the bottom hole in the forward flange of both utboard step ribs and the two corresponding holes in the bulkhead. Clecoed the bulkhead to the step ribs.