Power to weight your car is about 10.5 lbs/1hp. A 500hp vette (using C5' weight) is 6.5 lbs per HP. unless you're running a ~150 shot, I dont see it.
By my math (which is admittedly bad) you're guessing about 202hp? He did say it was a built h22a, i'd give him a little more credit than that. and to match the vette he'd only need about 350hp, which is very believable, considering built motor & a "decent" shot