Today's task was to dimple the forward bottom skin. A few dimples into the process I remembered that I hadn't removed the primer from the forward bottom edge for firewall sealant adhesion, so I took care of that task easily with the help of a little scotchbrite and MEK (photo 1).
The one hole where the bottom of the F-796B fuel tank attach bracket reinforcement angle attaches (aft end of the forward row of holes, photo 2) is called out on Drawing 28 as a #4 AN426, but on Drawing 38, a #10 AN509 flathead screw is called out. I'm sure the screw is correct, I just need to figure out whether to dimple the skins and countersink the lower longerons now, or wait and countersink the whole assembly later. I'll check some other builders' logs and see what they did and why.