LA360 or Magnum?

Is the magnum block superior to the 71-74 360 blocks? I have a 71 360 in my dart and everything I've read about them seems to point to these blocks being a little thicker. In a couple years I would like to build a motor up for auto-x or road racing so I'm curious if I should just stick with this block or go magnum. I've always heard the shaft mounted rocker system was better than the stud style but I'm open to all info. I also already have a new alternator and AC compressor for the V belt setup, I'm assuming I could keep that setup if I switched to a magnum?