The interference between the main longeron slots in the F-706, F-707 and F-708 bulkheads and longerons themselves has been bothering me so I filed about 1/32 out of the top of each slot. I only got the left side done, but now the top of the longeron fits flush to the top of the aft side skin without being in contact with the edges of the slots in the bulkheads.
I then match drilled the aft half of the F-623 left corner rib to the bottom skin. There was about 0.010 misalignment between the holes in the edge side skin bend and the holes in the bottom skin, and since I couldn't cleco through the undrilled corner rib, I drilled through the bottom skin only to 3/32 so I could re-cleco the side skin and final drill the assembly to #40 all at once.
Match drilled the aft half of the corner rib to the bottom skin on th left side.