Factual error: Neighbor states: '72 Challenger, 4.9-liter, V8. The '72 Challenger came with a 3.7-liter slant-6, 5.2 and 5.6-liter V8. (00:11:30)
Suggested correction: Sounds like the neighbor is mistaken, which would just be a character mistake. Remember, the car wasn't his. He had just inherited it, recently as Hutch points out. He admittedly didn't even know the correct 0 to 60 time.
Factual error: As many rounds that were fired at the Challenger, it would have died a lot sooner.
Factual error: The film begins and ends with Hutch handcuffed in custody, being interrogated by two police detectives. He was apprehended at the scene of a major violent crime with many fatalities, he has a gunshot wound, and he's a likely murder suspect. In real life, Hutch would be strip searched and treated for injuries under tight security, and he would not be allowed to carry personal effects into the subsequent interrogation. But during the interrogation, Hutch impossibly produces a pack of cigarettes and lighter, a can of cat food, a metal can opener and a live kitten from inside his jacket.
Suggested correction: You're missing the concept that he was a special individual. He would not be treated as you suggest, because of the uniqueness of his character.
His "special" status was unknown until the end of the film, when the two detectives simultaneously receive phone calls with orders to release him. Before that, he was still in handcuffs and being interrogated, and his identity was still a mystery to the police.