I took the advice of some smart fellow on the forums and dimpled / countersunk the tops of the aft spar flange where they join the W-707F / E doubler plates. I think that trying to dimple the combined thickness of both parts would be difficult after they are riveted together. After that it was a simple matter of taping off the holes that will be later occupied by rivets joining ribs / brackets and flap braces then squeezing a rivet in the few remaining. Next up is more rib preparation.
