iron heads for a 408?

Was thinking of porting a set of iron to flow at least 250cfm. I think I'am capable of doing that. But would 250cfm be enough to support 480hp in a 408 with a comp cams solid roller the .564/.570 cam. Then redoing the seats and guides. And cutting for the bigger valves.

In my head porting class I got a set of magnums to flow 244cfm at .500 and .600 lift. this is with 1.92int valve. I'am going to flow it again tomorrow after the porting I did today. Also are flowbench had clay stuck in the pedo tube because of idiots. And we cleaned out the tube and it is till 10 to 15cfm low. The reason we know this is a kid in our class brought his head and another head to his dads superflow 600 and it did almost 30cfm more. But after we cleaned the tube we got it down to only 10 to 15cfm low.

Our teacher ordered a new pedo tube. because there is still some clay stuck in the holes inside.