The only difference between LA, LA roller, or Magnum is how they oil, how they’re set up for camshafts (roller with holes drilled and tapped for a spider) and maybe some metallurgical differences with regards to nickel content. But I personally don’t think there is enough of a difference to make a significant difference in strength. Also people claim the magnums had better production machining practices and therefore are better but if you’re building an engine you’re machining it anyway.
The other plus is the magnum is much newer, often the first rebuild on the block. The LA cores are so old now, getting a virgin one isnt common. Just like the core I used for this build, it had allready been rebuilt 2 or 3 times before I machined it