Panoz has utilised a couple of V8 configurations.
I believe the early racing coupe had a Roush (Ford) of 5.8 litres displacement.
Current V8 is a Hendrick prepared and significantly modified (for durability) NASCAR motor (pushrod and distributor, but fuel injected, rather than Holley equipped).
Corvette runs very trusty 7 litre (427ci) all-aluminium ZLT6 - again with OHV. Simple, durable, lightweight and powerful - all good ingredients for an enduro. Their 6 speed Hewland transaxle will make a difference - but most of the gains on last year have come from their new Michelins. I figured a very close match with Prodrive. However pre-qual times that are 5 sec per lap quicker than the 550 suggests that, unless they run into unforseen mechanicals (which is quite rare these days) they will run away with GTS, which is a bit of a shame, as the rest of the race is shaping-up to be a bit of a foregone conclusion aswell. I did notice that the 'vettes put in more laps than anyone else, however - anyone who attended know why that was?
I reckon that those bad-ass C5's could give the Panoz a hard time, even.