loss of 100hp going to the wheels is not unusual with a RWD car, especially when it has to spin such massive sized wheels/tires. The Vette already uses an enclosed driveshaft so I dont think that will solve any issue at all. The transaxle and halfshafts are more likey the culprit. Anytime you have to turn your power delivery 90degrees there will be healthy loss.

You also have to remember the factory test numbers come from a test cell and not an actual engine in car. While they do account for accessory drives the state of tune for a particular car, plus the condtions under which it is tested (i.e. temp, humidity, fuel quality) can all be variable factors with lot of impact, especially on a supercharged engine.

All that aside, to roll into a dyno and put 500 ponies on the ground is stout for ANY car...exotics at twice the price included.