the Magnum is basically a Chevy
the oiling changed , no rocker shafts , they use ball stud type like chev so the strength is less & the rocker arm travel is limited by the slot in the arm unlike shaft type , the oil is fed up the pushrod from the lifters like a chev so you cannot use LA heads as there is no way to feed the rocker shafts oil. The magnum heads can be used on an LA block using AMC lifters & hollow pushrods . The intake is different as well , the La has angled bolts into the heads , the Magnum has vertical bolts so you cannot use an LA intake on a Magnum head .
Bolt pattern is the same for both but the balancing is different for a 360 Magnum as well .