The different kinds of models were thef100, f150, f250, and f350 and those were broken up into separate categories for the gross vehicle weight. They were for the f100 two wheel drive f101-f10 (4550-5700) gvwr. The four wheel drive f100s where f11-f13 (5250-6500) gvwr. The f150 two wheel drive was f150 and f151 (6050-6200) gvwr. The f150 four wheel drives where f140-f143 (6050-6500) gvwr. The f250 two wheel drives f250-f259 (6200-8100) gvwr. The f250 four wheel drives f260-f266 (6500-8400) gvwr. The f350 two wheel drives were f350-f359 (6000-10000) gvwr. The only classification for the f350 four wheel drives was the f360 (8550) gvwr.

These classifications are the amount the vehicle can hold with the brakes, motor, transmission, suspension,  and frame strength and drive line the truck had (four wheel drive or two wheel drive).The classifications can be found in the vin number on the outside of the door frame. The 73-77 trucks look mostly the same except a few differences.

Example of a 1973 f150 4x4 (not stock)

example of a 1977 f150 4x4 mostly stock

The main difference between a 73 and a 77 is the grille the 73 was more rounded and the 77 was squarer. And the emblems were moved from the lower fender to the cowl. There were also different options in those years in 1974 the first extended cab was introduced with a bench or two sideways buckets in the back row. In 1973 the super camper specials came out to accommodate the heavier slide in campers of the time.