Can it be done? Yes.
Should it be done? Maybe, maybe not.
I did it, and it was a lot more work than I anticipated. The LA block does not have the bosses on the front that the Magnum block has, so the power steering pump bracket and the belt tensioner bracket don't have a place to mount. You'll have to fabricate those two items to make the whole package work. Even if you're planning on working around the PS, I don't think that was an option for any OEM Magnum vehicles, so you're on your own for finding a belt that will fit. No matter what you do, you'll have to sort out the tensioner.
After sorting out the PS/Tensioner issue, finding a belt for my resulting system became an issue. The 7-rib belt that Mopar uses is much less common than the 6-rib belts used by GM - and apparently lots of other folks. You COULD use a 6-rib belt and just leave one rib open, but I was stubborn and figured Mopar had some good reason for using the extra rib.
There's also an issue with the upper radiator hose and T-stat location from LA to Magnum. The Magnum AC bracket covers part of the LA t-stat housing, so you'll get interference between the AC compresor and the hose. I ended up hacking off a corner of the bracket AND a part of the compressor to make it fit. I'll end up tweaking that aspect some time, but it's not a clean setup. A 79-up style intake MIGHT move the t-stat housing in the right direction, but I haven't tested that.
I made it work, but I don't know if I'd use an LA block if I had to do it all over again.
Clair