Worked to complete riveting the vertical stab skin. My buddy Kevin was in town for the weekend so we put him to work. Most rivets around the edges went well. We had some issues with getting the squeezer on the rivets next to the rudder hinge brackets. Tried different combinations of squeezer parts but could not get on the rivets squarely. Decided to buck them and had to modify a bucking bar to get the face square on the rivets. Got some to work but ended up with four rivets with the "club" shop head and part of the hole in the spar visible. Drilled out the unacceptable rivets and ended work for today. Did research on riveting in tight spaces and put out a call to a fellow builder in the neighborhood to borrow a thin nose yoke for the squeezer.