The long bed "Flare Side" is better to load field crops in, using the side steps (which the Style Side trucks don't have). Field crops include watermelons, cantalopes, and square-baled hay. PLUS 8' lumber. 8' beds are for "working", by observation. With a Chrysler-length wheelbase for that "good ride" to the worksite or field. Didn't see very many short beds on the farm, as I recall.
Back when that F-100 was new, there were many little things about what trucks sold where and with what equipment. Which related to the owner demographics and the agricultural make-up of the areas of the country.
Many fleet/cheap truck buyers would choose a Ford as they didn't have the historic issues with the column 3-speed shift linkage that Chevy trucks had. Most of the trucks sold east of the Mississippi River had factory back bumpers, but most sold west of the Mississippi had aftermarket "hitch/bumper pull" bumpers (which would relate to how many customers pulled trailers with their pickup trucks). Ford had their 300cid six-cylinder, but Chevys were more about V-8s.
CBODY67