That's silly! Do really believe they do a 1/4 mile test first and estimate the HP out of the 1/4 mile time? Of course not! Car makers measure the power of the engine at the crank, power figures stated in magazines/databases etc are always measured at the crank. After that they probably also measure it at the wheels to see how much power the transmission, crankshaft etc soak up on power.
horsepower IS measured at the crank, not the wheels. a 360 would beat this car with less power to weight anyway, even on a straight.
thats quite interesting, the reason the HSV loses such power is because of its rather stone-age drivetrain. generally, cars get heavier through the years as a result of adding safety features, and the things that make them bearable. this car doesent have roll bars, and its bodywork is quite thin compared to modern cars.