If the camshaft has 214 duration (which sounds about right with .449 lift) I would seriously consider just adding your magnum heads and zero deck the block and take advantage of those bigger valves and quench design. Your cam produces excellent low end torque and works with your stall speed, keep it. Really, how often do you see over 5500 rpm? Along with an intake (eddy air gap or simular), new valve springs, and pushrods, you should look into headers if you don't already have them. Mag heads flow worse than some la heads. Although you can easily gain a few cfm at home by cleaning the bowl and port of the heads.