I 'll be your huckleberry..........
You can build 600 Hp with virtually any 440 head ever made with enough time, money and know how. The question is how you do it. ALL of the aftermarket heads will do it. Most with ease. Questions that need asked are as follows

1) what parts do you presently have? Be specific. It was gone through but by whom and what parts were used? The more info you give us the better advice you will get.
2) what is the budget?
3) We know it is a 440 in a Road Runner. But if this is for street stomping is it to be pump gas? or race gas? Do you know how to adjust valves? What gear in the back? If for the back road 500, what is to be done about brakes, steering, cooling and exhaust?
There are about 50 questions that I could ask you before we get to what specific cylinder head. There is a bounty of people here and on other sites like this one who can and will help you with advice. If you are new to old Mopars welcome. But advice given here or anywhere totally depends on how much information you can provide and how you choose to use it Slow your roll a bit
Just saying