Successfully complete the game on Golden Days, then save after the credits complete. Then, start a new game on Golden Days. You will now have the '59 Impala as well as the '61, '63, and '64.
Successfully complete the game on Golden Days, then save after the credits complete. When you return to the main menu, go to Arcade Kings and the "Unlimited" option will now be available. You can compete against the CPU or a second player using the cars that the CPU used against you (for example, Chill N62, and the car with horns).
Press L1 or R1 to change color of your rims (gold, silver, etc.).