Thanks, G, and Sluggo.
What I'm getting here is that First Class was the first four rows, with two seats apiece on each side of the aisle. That make for sixteen seats total in First Class.
But, how were the rows numbered? Does the numbering system start in First Class, with Rows 1, 2, 3, and 4? Then continuing in "Tourist" as 5, 6, 7, etc.?
If so, then the Tourist section is numbered 5 through, what? There are some problems in the diagram on the pictured 727-100.
I count 17 rows in "tourist" on the port side of the aircraft, which makes for a total of 21 rows in the aircraft when added to the four rows in First Class. So, are the rows in Tourist numbered 5-21? If so, what happened to Row 18 being the last row? Where was D Cooper sitting?
Note: the rows on the starboard side are off-set by the galley.
This also makes Larry Finegold's statements more troubling. Since Larry was in Row 6, which is by the galley AND he had a conversation with G-Man Johnny, that means the FBI agent had entered into the aircraft about a third of the way, since the forward entry door was in front of Row 1 and the "wind screen." Hence, this was not a minor incursion.
Plus, I don't see any jump seats for the Fight Attendants, other than the two-seater in the forward section. Where was Florence sitting? I thought she was aft of D Cooper, sitting in a jump seat in the aft galley, as is typical in most planes these days - but there was no aft galley in the 727 as pictured, and the only galley was mid-ship.
Lastly, my understanding of the 727-51 designation meant that this plane was part of the Northwest Orient fleet, and was in fact a 727-100 series model.
Bruce, The fellow who tried to board the aircraft to talk to Cooper was an FAA man who thought it would be a good idea to tell Cooper that he could find himself in a lot of trouble if he hijacked the aircraft. I suspect that Cooper already knew that. In any event, the individual was removed from the scene.
The -051 was specific to NWA but it was still not a 727-100 aircraft. If it had been an NWA 727-100 it probably would have had a -151 suffix.
Thanks for posting and finally clearing up the large issue on the FBI COWBOY VS FAA FAA FAA ... MAN MAN MAN!
Bruce doesnt believe anything I say.
So, here is the cigar of the airplane. PLEASE PLACE THE SEATS IN THE CORRECT CONFIGURATION. Lets get that issue settle too finally...
G. 
Bruce doesn't believe anything I say either but here is another try at explaining the seating configuration.
At the right side of the cabin diagram, you see the aft stairs. Then moving to the left, which is forward in the cabin, the head is indicated by the "L" and the galley by the "G".
Row 18 is the first row forward of the head and Cooper was seated in 18E which would be just forward of the letter L. Tina spent some time in the aisle seat 18D and Cooper had his brief case with the bomb in seat 18F.
Mitchell was apparently seated in 18B just forward of the letter G and had his books in the aisle seat 18C and his coat in the window seat 18A.
The seat rows count down moving forward (to the left) in this illustration. There is no information about additional galleys or heads in the cabin but my guess is that there was another head at the forward end of the cabin near the cockpit door. I doubt if there was a second galley on the aircraft.
The exact number of rows in the first class section (with four seats across) is not known. But there was a divider of some type between the first class section and the start of the tourist section (with six seats across). This divider included at least a curtain and probably a bulkhead of some type. There may have been a closet type of arrangement for the first class passengers at the very rear of the first class section. The unwashed passengers in the tourist section would have to put their coats in the overhead bins or on an empty seat (as Mitchell apparently did).
But the first row of seats aft of the side entrance door near the cockpit would be the first row in the first class section and was Row 1. The row numbers then would count consecutively up until reaching the last row at the rear of seats at the rear of the cabin and that was Row 18.
If there were four rows of first class seats with four seats per row, then there would be 14 rows of tourist class seats with six seats per row. This would give the aircraft a capacity of exactly 100 passengers, plus a three person cabin crew, and plus a three person cockpit crew.