Need to be more specific, but I'm betting that a 390 Holley would be best for your build and level of experience. Why do you like the 570 so much? What are you basing your opinion on?
"Boring the engine", "upgrading the cam", and "Offy intake and headers" are all very generic hop-ups. What is your target compression ratio? What are the exact specs of the cam you intend to use? What rear end ratio? How much does the car weigh? If you're using an automatic transmission, what's the stall speed of the torque convertor? What do you expect the car to do when you're done (do you have a specific horsepower goal, specific quarter mile time, mileage expectation, budget?). Until you have very specific answers to these questions, you're just shooting in the dark. Just searching the web for parts is FUN, of course, but not really all that productive... :)
Think of a car like a football team. A great quarter-back (or even two or three great players) won't take a team to a bowl game. Not only do several key players have to be good, but they all need to play well together and compliment each other's strengths and weaknesses, and you have to have a a great playbook for them to execute.
Best of luck!