I'm using a Dura Spark II from a 78 Fairmont, new from Auto Zone, with the MSD6 control box and it works great.
The new distributor, cap, adaptor, rotor, wires and MSD6 all came to about $300 so it's a little cheaper. If you go junk yard route or if you connected via a Dura Spark or GM control module you could do it for much cheaper and still have a very effective ignition.
Mike Raley claims excellent horsepower additions from the change to the DUI from the same set-up as mine though so if your looking for performance the extra cost for the horsepower gained is worth it.
If I hadn't already went with the new Dura Spark and MSD I would go with the DUI.
Bob