Bob and I caught up the left tank to where the right tank was. We washed all the parts (skin, attach points, ribs and stiffeners) then we went to the straight back-rivet method and it went much faster. We back riveted all the stiffeners in the left tank, then formed the sealer fillets and encapsulated the rivet shop heads. Then we installed the filler flange and drain - encapsulated those shop heads and fillets, then sealed the reinforcement ring, plugged the tooling hole and made the 1" increment lines on the fuel filler bay rib - and bam-o we were done!
Of course, we didn't have to finish & rivet the trap door as there is a standard fuel pickup on this side, but the regular back-rivet method is the way to go. Thanks again Bob!