For a kick in the pants on a budget I would either

1. put in a 440, or

2. heads, intake, cam, headers on the 383 if compression checks out on your motor

Either would be a significant upgrade from what you now have. You don't always have to spend 7-8k on a new mill to improve performance and have fun. Spend the other money on brakes, and holley sniper fuel injection to get the modern performance aspect you mentioned.