There were five generations of this car. The first was only around for 1967 and 1968. It was a 2 door hardtop, but I would resist calling it a coupe due to its large size. The 4 door version was called the Brougham, while the fastback and convertible versions sold under the name Park Lane. All engine options were V8s, ranging from a 390 cubic inch up to a 428 big block making 345 horsepower.
The second generation of this car lasted from 1969 to 1972. It featured the 429 cubic inch V8 engine with a dual carburetor setup. There was an option for a four barrel 429 engine taken from the Marauder. The only transmission option was the 3 speed automatic.
By the third generation, which lasted from 1973 to 1978, this car was really getting huge. It was now sold as a 2 or 4 door hardtop or as a 4 door station wagon.
The fourth generation Marquis was from 1979 to 1982. The car had a more boxy look up front to fit in with other cars from the time period when aerodynamics were well-known but openly ignored for some reason. This car was smaller than previous models and got a smaller 302 Windsor V8. There was a 351 Windsor option, but few people bought it. Those cars are very rare and highly sought by collectors today.
In the final years, from 1983 to 1986, the Marquis was switched from the Panther to the Fox platform. This meant that it was closer to the size of a Ford Mustang than it was to the larger Grand Marquis. The 2.3 liter Lima I4 engine was the standard on these cars, a big downfall from the days of the 429 cubic inch V8.
Some of these cars are collected, while others just collect rust in a junkyard. You can find good deals on a restored 1968 Mercury Marquis classic car or an unrestored Marquis project car by taking advantage of the size of the internet. Search on eBay for these cars and their parts. The prices are very low compared to what you'll pay elsewhere.