I use these guys when on my buying trips/vacation in the USA.
http://www.arguscarhire.com.au/
Online global booking- Ezi online system to check prices/insurance etc..[ I use the Gold option]
Ive never had an issue. They use multiple rental companies, so your guy might be best to call a local office to him to check the vehicle options. They use a random system as to who rents you the car. So it could be Dollar, or Alto etc. Most have a Challenger or Mustang but best to check.
I have found them to be the best value and they supplied a one-way mini van for my wife and I when we drove NYC to LA on a 3 week vacation,with no one way fee!
cheers Dave