Economy Class Seating On A Pan Am 747 In The Late 1960's
imgur.com
imgur.com
http://www.calgaryherald.com/business/cms/binary/7939683.jpg
Without sufficient power, the airlines lowered the amount of allowed weight on allowed on international flights and thus the seats had better spacing. Later models starting form the -200 model had more powerful engines so they crammed in more passengers - both in coach and in first class.