Fastened the rudder horn onto the rudder spar and final drilled the four holes through the upper edge of the rudder horn. Clecoed the rudder horn to the R-904 bottome rib to check fit. I had to radius the top of the rudder horn so that it fit the radius of the rib flange. Clecoed the R-904 bottom rib and the R-405PD rudder horn to the R-902 rudder spar. Slid in the R-917 shim between the rudder spar and rudder horn. Then drilled all the holes to #30.