The Mustang underwent a complete redesign in 1971. It grew bigger in every way compared to the first generation model. The second generation was 7.1 inches longer, 6.8 inches wider and 500 pounds heavier. Mostly it seemed bulkier. The hardtops had a high trunk and a tunnel back window. This Mach I was donated to the museum in October 2017 by Joseph Ruffner of Ventura. You can always see this prize winning Mustang in person at The Murphy Auto Museum too.
Here's the Hagarty value for this car.
Watch an old TV Commercial for the '71 Mach 1.