Time for some more back-rivetting to attach 3 pieces to the top skin prior to attaching it to the top side skins. The manual specified 3-3.5 rivets for everything, but the skin doubler/fuselage rib/top skin interface definitely needed 3-4’s.
I find it easier to align the gun with the long back rivet set, combined with a block of wood with an end cut perpendicularly to line up on.
The F-14131 Aft Fuselage Upper Rib had to be gently flexed to allow the gun correct access to the rivets, but didn’t seem excessive. Worked out just fine.