I got some professional help with the longerons from Riley. She helped me drill the right side after marking the holes and we managed to get everything lined up beautifully on that side. The edge distance on the right side was just fine. The important technique was to realize that the aft part of the gusset wants to rotate inboard. Simply pulling it outboard when drilling the holes fixes the edge distance problem.
After the right side went so well, I went ahead and remade the left longeron and attached it with my new techniques and that side came out much better.
Berck: 4 hours, Riley: 2 hours.