Spooky 2,
How very odd??
All 21 Qantas -320 were -320C, ie -338C, and Oh! Boy! did they have a high empty weight, compared to a passenger -320, yet only two of the QF aircraft ever operated as freighters in Qantas service.
Somebody had the bright idea that they would be more re-salable (spelling?) as freighters, so we burnt a lot of fuel to support the re-sale price years later.
Maybe NW was just as dopy, buy a cargo door, but save weight with a passenger floor.
Best one I ever flew was a -321C, one of the last B707 built, delivered new to PanAm, a dedicated freighter, it had a very nice low empty weight.
It came to my then employer from a Texas mob, Maverick Ranch, and the cargo door liner said, in letters that covered the whole door: Maverick Ranch -- World's Biggest Bullshippers".