Cleco the skin to the lower side of the stabilizer assembly. Drilled all the ribs to a #23 and then reamed the holes to a #21. The pilot holes were a little off so I wanted to undersize the holes before drilling to the actual size. Removed the skin and flipped the stabilizer assembly over and cleco the skin to the top side. All the ribs only have pilot holes on the top side as well so these will need to be drilled to a #21 for the A5 rivets also.