Himms is apparently misinformed. Ralph has a lot of details wrong, and I have a whole list in my notes. Remember, too, that Ralph was not the principal investigator in Norjak early on. He only gained prominence in Norjak in 1975 for the John Doe file at the Federal Grand Jury in Portland. SAC Julie Mattson clearly ran the Cooper show in Portland in the early days.
As for seating arrangements, according to Bill Mitchell in multiple interviews with different sources, WHSM, Galen, etc, he was sitting in 18-B and Cooper was in 18-E, although the skyjacker might have initially been in the aisle seat, 18-D, when he gave Flo the note upon take-off.