Only sure way to get a V8 is the adrenaline collection or some of the big Tahoe's or similar.
Used the AC for 7 years, never always got what you specified, but now you cannot specify a specific model, but you will get either a Mustang GT Camaro SS or Challenger RT
Had a new GT a few weeks back, had a few toys, line lock was great fun
Was a 2019 model with 450 bhp and the new 10 speed auto box