Clecoed support bracket assembly to left inboard seat rib and test fit slide tube and friction block. Fit cotter pins and F-8119E connector plate to slide tube. Blind riveted support bracket assembly to left inboard seat rib. Discovered rivet section error on tube guide assembly - used CS4-4 instead of LP4-3 blind rivets. That would explain a lot; why dimpling/countersinking wasn't called for, and the poor mandrel breakage. I should have double checked, instead of grabbing from what I thought was the right bin. DOUBLE-CHECK RIVET CALL-OUTS. It's a lesson I should have known by now.