Installed two F-00773A stiffeners to the interior of the tailcone skin, directly below the access panel under the horizontal stabilizer, one on each side of the airplane, per Vans Service Letter SL-00014. Deburred stiffener edges and holes, and scuffed, cleaned, and primed the faying surface. The interior of the F-773 aft side skins had already been primed. Rivets Today: 10