Is this right

I would guesstimate that to get 490hp you would need mildly ported W2 heads or heavily ported Edelbrock or RHS heads. 850CFM carb

And it would be a 7000RPM + engine.

However I've never built one so I could be wrong.

If it shows an actual horsepower/torque curve you can tell straight away if it's bogus if they don't cross over at 5250RPM.