I think the 240cc runner if the dart heads you are looking at would be too big. I am getting ready to build a pump gas 572 and AFR only recommended a 335cc runner head for that motor being taken to 6500-7000 RPM. My dad and I are also in the process of building a pump gas 496 being rapped to 6500 RPM. I spoke with comp cams and some motor builders around here, and they said that I was on the fence as far as if I should go with ovals or rectangular. Pretty much the ovals will have more torque and the rectangulars will have more hp. We decided to go with a set of 781 ovals that we had polished and ported and fitted with 2.19 1.88 valves. We got a custom grind comp cams mech roller with duration in the 265@.050 range and .650 lift. They said that that motor with that cam should make power to 6500 RPM. Another thing you might want to think about. If you decide to go with a set of Rectangular heads, I would look at the AFR 315cc head. They are $3000 for an assembeled, 100 % CNC ported set, but I talked to AFR, and they said that they built a 496 with that head that made 750 hp at 6500 RPM on 10:1 compression and pump gas. The AFRs are $1000 more than the heads you are looking at, but for a CNC ported dart BBC head, It costs $4000, so in that light it isnt so bad.