Not quite true. Up to 2002, the JGTC NSX was based on a factory NSX unibody. Honda removed the front and rear subframes and replaced them with a full-race tubular frame and pushrod suspension. They also hacked up the rear unibody to install the engine in a longitudinal orientation. The engine powering these cars was a normally-aspirated factory C32B block and heads, increased to a displacement of 3.5 liters via a stroker crackshaft. The engine was fed by a ITB system with functional snorkel and produced nearly 500 hp. Aside from perhaps the turbo Le Mans NSX-GT, these cars were the most radical iteration of the factory NSX design in the world.
Due to evolving JGTC regulations (now called GT500), in 2003 Honda abandoned the factory unibody and built the car using a pure tubular race car frame sourced from Formula Nippon. They also switched to a turbocharged C30A for power. It is these cars that are most like NASCAR, since they are nothing more than a NSX-shaped fiberglass shell on a tube-frame race car.
Thus, to me the last, greatest NSX's were those original JGTC race cars. Just goes to show the incredible potential of the original platform. It is nice to see the old design set a course record. The only US offering I have seen come close is the FXMD Time Attack NSX, but even that cannot compare to the JGTC cars, which were factory-backed and developed. Though, I bet with a similar budget, Shad could build you something equivalent.