Magnum uses a serpentine belt drive so most items are mounted to the front cover as opposed to the LA.
So the alternator which is a small nippondenso unit and the small a/c compressor mount in different locations on the Magnum.
Not the same.
Not completely true. Yes, the alternator mounts in a different location completely, but an LA alternator bolts right up to the Magnum heads just like @Dartsun said above.
But the tensioner mounts to the front of the head, and the PS pump (if used) mounts to the head or the head and block depending on the case. Jeeps use a bolt on bracket that mounts to the head only while the Ram bracket uses a boss on the block that the LA block doesn't have.
So, LA accessories bolt to a Magnum just fine because the necessary bosses are there and in the right location, but the Magnum accessories will not work on LA heads because at the very least the tensioner can't be bolted up.
As another example, I am running Magnum R/T heads on my numbers matching 360 LA block and the stock alternator bolted on fine. But I know the truck or van PS bracket will not work on my car because of the missing boss on my block.