That was in the days when the U.S. government strongly regulated the airline industry -- routes for airlines were largely fixed in place, fares were high, and airlines had to compete mostly in terms of passenger service. Passengers, in turn, usually dressed up when on an airplane journey, men wearing jackets and neckties.
As can be seen below, Douglas DC-8 airlines had large windows, one per row of seats, giving passengers a fine view if a view was available. But this amenity, which provided plenty of legroom, prevented operators from increasing the number of seating rows. That "error" was soon corrected on later aircraft, as those of us who usually fly in "steerage" well know.
Below are some views of DC-8s and their accommodations.
This is an early photo showing Eastern's livery at the time it started flying DC-8s. Note how large the windows are. DC-8s had one window per side for each row of seats. This amenity prevented the addition of rows of seats that was possible for rival Boeing's 707 that had many smaller windows, a feature found on later-generation airliners.
It took several years before ramps from terminal waiting rooms to airliner doors became common. Here passengers are depicted using roll-away stairways.
This seems to be featuring the first-class section.
Although the DC-8 was designed to seat cabin-class passengers three-abreast on each side of the center aisle, SAS had three-and-two seating on a least some of its DC-8s. So the seats shown here might be a little wider than on planes used by United Airlines and other American lines.
Another publicity photo of cabin-class. Note the leg room, the window curtains and ... oh yes, the snack being served.
I'm not sure if this is the first-class section or the three-plus-two seating arrangement. What's noteworthy in this photo is the overhead compartment. Luggage, coats and such would usually be stowed (tossed, actually) there, but here we see mostly SAS-furnished blankets, pillows and such.