Where magnum generally have an advantage is the short blocks are usually in decent shape and the pistons are high enough to build ok CR and the ability to run a hydraulic roller if one chooses, basically you don't have to do a rebuild, the magnum heads in stock from seem to respond a bit better to a basic hop over stock 1.88 360 heads. Obviously there's the head cracking problem which maybe an issue depending what your doing, and the lack of oiling for LA styles is a bit of a pain limits upgrade or makes it more expensive.
To me if adding parts to a running engine, magnum shines, doing a full rebuild doesn't matter as much.