Big caution regarding using this cam with magnum heads. There is only one valve spring currently available for the Magnum head that does not require machining the seats on the head. This spring is the Magnum R/T spring from Mopar Performance and it will not support the .520/.523 lift you get with the 1.6 ratio rockers the magnum uses and agressive profile on this cam. The XE274H cam is the cut off point where you now require a dual spring to control the valves and Comp told me the MP R/T spring was not acceptable for this cam.
I am doing pretty much the same build and I am using the XE268H cam p/n 20-223-3 224/230 .477/.480. This cam is acceptable with the R/T spring per the Comp Tech Line.
NOTE: what ever way you go you will need to purchase new retainers. The stock magnum spring is smaller in diameter at the top and the stock retainers will fall right through any of the springs recomended for the LA head. These retainers will also almost fall through the R/T spring. Either order the retainers and locks spec for the R/T spring (or high lift spring) in the MP catalog or save a bunch of money and use 2.2/2.5 mopar 4cyl retainers with the stock locks (your magnum locks, not the 2.2, they are multigroove or not in the same postion). Remember the valve stems on your magnum valves are 8mm not the 3/8" on an LA head so you will have to search for a retainer. Comp doesn't have a retainer for this size stem that works with any of there LA springs.