Can i use a LA timing chain set in a magnum engine?

The short snout on the Magnum camshaft eliminated ONLY the ability to mount the fuel pump eccentric. The timing chain still sits on the camshaft exactly the same. With the snout shortened and fuel pump eccentric removed, they also changed the camshaft gear washer arrangement.
An LA timing chain will fit a Magnum short snout camshaft, you just have to check the fit and use the correct bolt and washer. If the snout sticks out past the cam gear a little, you need a cup style washer to clear it. If the cam gear sticks out past the snout a little, the flat Magnum washer and bolt will work. Always check this and bolt length before running a bolt in and calling it good.
If you want a mechanical fuel pump on a short snout camshaft you just add the adapter kit like Hughes Engines sells and secure it with Loctite during final assembly with the supplied cup washer to clear the adapter.