You may use any unmodified road car. The Jag XK-220 and the GT-one Road Car are both eligible.
I would suggest the Lotus GT-350 with T2 tires.
With a nice, smooth driving style you will win easily in this car.
The NSX is another good choice. If you use it, put a set of T2-T3 tires on it. Then the other NSX in the race will lose to you on pit strategy.