After much deliberation, I decided to turn the H/S on its side to buck the inboard rivets (I used a offset shank). The results were as good as can be expected when bucking a -4 rivet (see 1st picture). Also, I pop-riveted the middle rib and attached the spar to the end nose rib as well as attaching the end main rib to the spar.
I noticed that the rivet holes on one side of the end rib did not line up perfectly with the skin. I spoke with my technical advisor (Dad) and he told me that this is common. Additionally, he told me that the best path through this issue is to use a punch on the hole above the hole you are riveting to "pry" the hole into alignment while you are squeezing or bucking the rivets. As you move down the line, the holes will line up. Also, this method will work to align the rib tabs to the skin holes. That being said, do not re-drill the holes.
