Yeah, it's plenty good enough to win the All American GT, and you probably won't even need to buy harder tires, unless you're hunting for points. However, be advised, this car devours its front tires ruthlessly under hard braking and cornering, so you'll need to be pretty mild and early on the brakes to keep it from killing you. It's also not a major concern in this particular championship, but the fuel economy isn't the greatest, either.
And, in my opinion, you should drop that St.3 tuneup. You won't need the extra power (except maybe at New York, if you're facing the Panoz), and it'll only serve to devour your tires a bit faster.
However, for a cool million, it's a great racer.