Help me decide part 2

I'd say that with the stock, unported heads you will not reach your 500 ft-lbs target, more like 450-ish, but I see that you're planning to use the Magnum exhaust manifolds. Might be even less than that.
No way you will hit 6000 rpm with that combo. The Edelbrock heads surely will help to get you closer to your targets, you might even step up the cam one notch.
Others with more experience will sure chime in.