The first thing you notice is the style. It's huge for a Mustang, and the bloated styling is polarizing. I happen to like it, it's sleek and very, very muscular.
The engine, despite its 351 cubic inch (5.8l) displacement, is lackluster under about 3500 rpm. We had it rebuilt, and when its enters its powerband at about 3500 rpm, it feels like God kicked it in the butt. The reason it has to wind up so much is the 351 Cobra Jet engine: it has MASSIVE ca. 2.5 inch intake valves and 1.9 inch exhaust valves, combined with intake ports approximating those on big-block engines. With C6 automatic and 3.25:1 gears, 0-60 is firmly in the 6-second range, and the 1/4 mile is probably in the high 14's or so. With the 5-speed and 3.55:1 gearset later put in it, both could be cut by a full second. A torque mill it is not, but it is one of Ford's best high-performance engines.
The C6 automatic was rebuilt as well, and shifts extremely firmly and quickly. Under part-throttle, it tends to shift a bit too soon, although with gas prices where they are, maybe that's not such a bad thing. The 5-speed built by Tremec which we replaced the C6 with had long, notchy shifts, but suited the peaky powerband of the Cobra Jet much better.
The interior is in somewhat rough shape and parts are not as readily available as for '65-'70 models, so be prepared to comb ebay, swap meets, and do some improvisation. For the chrome trim, we put on aluminum tape with good results. Fake wood veneer is easily put on the wood parts, and spray paint takes care of the rest. From a design standpoint, the dash is more ergonomically correct than previous models, but unfortunately it's all plastic. Also, the dash sticks up very tall and with the (sexy) fastback styling, it's a bit hard to see both forward and over the shoulder for lane changes. In other words, anybody shorter than 5'7" need not apply. The front seats are plenty comfortable, but the practical fold-down rear seat should basically just be left down and reserved for punishment for anyone over 6 years of age.
The suspension needs new bushings - it squeaks, even after a new suspension was installed to take care of the original setup. Otherwise, the 3400-lb car handles very well, although it rides firmly, bordering on punishingly. We chose 620lb front coils and 4-1/2 leaf mid-eye rear springs from Mustangs Plus. Curiously enough, this exact same setup elicits a far more agreeable ride in a lighter '68 Mustang we have.
Other than that, the problems we have had were due either to age or the fact that the previous owner never saw fit to maintain it.
Gas mileage sucks, its tremendous thirst compounded by its picky taste: it pings with anything but the highest-quality premium-grade, usually from Shell or Unocal. But if you're seriously looking at this, you didn't seriously care about that, did you? If you have to know, its 13/city, 13/freeway, making for a (do the math if you don't believe me) 13mpg average!
The car is devilishly fun to drive and is faster than it feels. If you're patient enought to let the engine have its head and build up revs, putting your foot into the throttle rewards you with a firm push into the seat and more than a few thumbs ups.