had to be retracted when opened downwards as a tailgate. Coinciding with the addition of 5-mph bumpers, Ford and Mercury station wagons underwent a major redesign for 1973, including a completely new roofline. In place of the framed doors, the station wagons were marketed as "pillarless hardtops"; though the roof was fitted with slim B-pillars, the doors were fitted with frameless door glass, a revival of an appearance offered from 1957 to 1960. Although slightly narrower than the 1959–1960 generation by , this generation of the Colony Park would be the longest and heaviest station wagon ever sold by Mercury. Due to its nearly curb weight, the standard engine was a 400 cubic-inch V8 with a 429 cubic-inch V8 as an option; in 1972, the 429 was replaced by a 460 cubic-inch V8 sourced from Lincoln. For the 1978 model year, a 351 Windsor V8 became standard (outside of California and high-altitude areas), with the 400 and 460 as options. However, most surviving examples are equipped with one of the two larger V8 engines, as they were far more popular, with the 351 proving to have little fuel-economy gains. Approximately 7,850,000 full-size Fords and Mercurys were sold over 1969–1978. This makes it the second-best selling Ford automobile platform after the Ford Model T. Sales Sixth generation (1979–1991) For 1979, Ford redesigned its full-size sedan and station wagons; the Ford Panther platform brought Ford in line with the downsizing introduced by the 1977 General Motors B-body full-size cars. To remain competitive (in terms of size and fuel economy) with the Buick Estate and Oldsmobile Custom Cruiser (1978 marked the end of the full-size Chrysler Town & Country station wagon), Ford made extensive changes to its full-size station wagons. In terms of size, the 1979 Colony Park shed over 11 inches in length, 6.6 inches in wheelbase, 0.4 inches in width, and had lost slightly over 1,000 lbs in weight (in comparison to its 1978 predecessor). Though technically smaller than the "intermediate" Montego/Cougar station wagon, the Colony Park reduced its cargo-carrying capability only slightly over the 1978 Colony Park. As before, 8-passenger seating remained standard equipment. In a revision of the Mercury product range, the Colony Park was moved to the Grand Marquis model line, the flagship of the Mercury brand. Effectively, it placed the Colony Park above its Country Squire counterpart in terms of trim; as well, this decision cleared room