The final of the big block Mustangs was the 1971 429 Super
Cobra Jet. These cars may have been designed to hold huge engines, such as Ford's coveted 460 cubic inch monster, but emissions standards prevented the company from achieving their ultimate goal of a beastly Mustang. In 1972 and 1973, the 351 was the largest engine option available. Ford was busy developing the next generation of the car for 1974, in hopes that the car's body would finally fit in with the times and hold a engine without enough empty space under the hood to house a small family. The performance models for 1972 were the 351 HO and the 351 Cobra Jet. They performed well against their peers, but they were a shadow of the cars the original Cobra Jet and the Boss Mustang had been.
Although fans were not happy with the changes being made to the Mustang, many of them have come around to cherish these early 1970's cars. They do not fetch the prices of the earlier models, but they are collectible, especially the performance models. You can find them listed on eBay, along with plenty of parts.