D.U.I is Davis Unified Ignition, it's a souped up ( for lack of a better term ) GM HEI, nothing more. MSD would give you more, cheaper. fire a GM HEI with a MSD 6A box. D.U.I's are great for engines in which there all that is available ( 200-250 I6 Fords, it's them, factory Duraspark which could be fired with MSD, or Mallory Unalite )