THEFED. If your looking for 500HP, it's called $$$$. If you want the 425HP range, it's easier.

I had a 383 in my Vette and it was super. A lot of torque. I had a speed shop in S. Amherst, Ohio build the motor and price wise it was very reasonable. If you want his name, e-mail me. He's built ALL my motors since the 60's.............