It's not all in big ports or flow #'s or material that there made of. But more so what the engine needs and wants. Like what lift cam are you planning on, how much compression ratio, what intake manifold, and carb?
You have to look at low and mid lift #'s not just peak, because this is where your camshaft is going to be running most of the time. It's far more important to have very good low and mid lift #'s below the cams peak lift than something higher than the cam actually opens the valve.
The 440 source heads show 290 cfm @ .600 peak on the int. and 220 @ .600 on the exh. and this is with a 212 cc int. runner. A set that I did with a 452 head and 2.14 valves which are the smae size as the stealth heads flowed 293 @ .500, more air at .100 less lift. And the port volume was only 186 cc's. I also did a set with port size compareable to the stealth heads @ 213 cc's and they flowed 300 # .500 lift, and this was still a factory casting, 906. Now the factory HP MP Max Wedge heads are 210 from the factory and with a minor cleanup of the ports, just at the gasket and taking the flashing out in the bowl and they flow 314 @ .500 and 343 @ .600, the exh. went 240 @ .500 and 253 @ .600. So in my book it's hard to compare the old cast as stock to a aftermarket head with revised ports. But when you compare the new aftermarket heads with new factory heads both in the same conditions they don't fare so well.
But in any case, it's not how much they flow at peak but whats under the curve that counts. What needs to be found out is what the stealth heads flow @ .200 and .300 and .400 lifts. This is what a 452 head did with a gasket match and bowl blending.