"The Mark IV carried over many design themes of the Mark III including the grille and faux spare tire trunk lid, and grew both longer and wider — sharing its platform with the Ford Thunderbird. In 1972, Lincoln introduced the small oval windows, marketed as opera windows, at the roof rear quarters. The 1973 model year featured front bumpers to comply with new US safety regulations...1974 models featured redesigned rear bumpers under mandatory federal safety regulations. It was the heaviest series of all generations.

Mark IVs were powered by a 460 cu in (7.5 L) V8 engine." Wikipedia