Be lucky to break 600 hp, probably more like 575,???

That cam @ 265 intake is smaller them the MP 590 @ 271 @ .05 you were using. But with the new engine you will be making a lot of torque. To make HP you need to spin them a bit. Your not going to be able to spin that new engine very high in its hp band with that small of cam. It will be done by 6000 rpm. Typical 500" motors with your comp can hit around 600 HP with the mp 590, your using a even Smaller cam.