Complex sentence: For 1981, as the Mercury counterparts to the Ford Granada, the Cougar line was expanded to a standard coupe and four-door (to replace the Monarch); the expanded Cougar line closed in on the price range occupied by the Zephyr.
Split into simpler sentences: For 1981, as the Mercury counterparts to the Ford Granada, the Cougar line was expanded to two-door and four-door sedans to replace the Mercury Monarch. The expanded Cougar line closed in on the price range occupied by the Zephyr.