Machine countersink nutplate rivet holes and installed nutplates on F-1204 center section assembly (page 20-02, step 1). Final drilled #11 bolt holes in F-1204CL-R forward bulkhead side assembly and left leg of F-1204 center section. Holding off installing retainer blocks until parts are primed. (page 20-02, steps 2 and 3). Machine countersink F-1204 center section that receive AN426AD4 rivets. Also, dimpled corresponding holes in F-1204D center section aft bulkhead (page 20-03, step 4). Deburred F-1204D bulkhead and holes in F-1204 center section bulkhead.
