The sixth-generation Ford F-Series was introduced for the 1973 model year. Known by enthusiasts as the "Dentside," the F-250 was based on the 3/4 ton chassis, whereas the F-150 was based on the 1/2 ton chassis. The F-250 was offered as a regular cab, a two-door Supercab, and a four-door Crew Cab with the option of a "Styleside" or "Flareside" bed in long or short bed configurations. Both beds and cabs could be optioned as a two-wheel drive or four-wheel drive platform. Engines offered were a six-cylinder 300cid, and five V8's throughout the years, 351cid, 360cid, 390cid, 400cid, and 460cid. Transmissions offered were automatic, three-speed, and, later, 4-speed, manual depending on engine and drivetrain. The enthusiast adopted model series name, "Highboy," was only sold as a 4x4 F-250 long bed in regular cab and Crew Cab configurations. The F-350 did not offer a 4X4 drivetrain until 1979, and the F-250 "Highboy" filled that void. Although the term "Highboy" was never used by Ford, the "Highboy" shared many components like the cab mounts, suspension, axles, and larger frame of the F-350. These trucks featured a divorced transfer case and Dana 24 axles and 4.10 gears. 4" lift blocks on the rear axle and larger front springs brought the truck to a ride height of approximately 3" higher than a 4X4 F-100/F-150 and 6" taller than a two-wheel drive F-250. All "Highboy" trucks had F26 and F28 in the Vehicle Identification Numbers. All models could be outfitted with any three available trim levels, including the entry-level Custom, mid-level Ranger, Camper Special, or top-of-the-line Ranger XLT and Ranger Lariat. The Camper Special trim was not offered for the F-250 "Highboy" due to rollover risk. For 1978, square headlights replaced the previous models' round ones on higher trim package models, such as Lariat and Ranger, and in 1979 became standard equipment. 1979 would also be the last year for Sixth Generation production, with the Seventh Generation F-Series replacing it.