There is another thread here about the same unit:
http://www.forabodiesonly.com/mopar/showthread.php?t=166982
Like I said there, it is not a bad part for the price. The term "HEI" gets tossed around a lot, but really that is only a GM item. That unit is more like a Pertronix is electrically. The trigger is bigger with more iron, so the electronics are mounted under that chrome cover.
The old mopar box on the firewall is similar in function to the GM HEI, the Pertronix, Ford TFI, etc. They are all electronic "switches" that replace the points. None of them are CDI ignitions.
Since the Pertronix is mounted inside the distributor, it runs close to engine temperature. They seem to work fairly well in that location.
The HEI in a GM car is bolted to the distributor body for a heat sink - they will fail if they don't have a big sink. I know GM owners that carry a spare & the tools to change the module because they crap out all the time.
Plenty of people here have had the mopar box or pickup fail too. As I said in that other thread, the mopar box you buy today is made in china just like this distributor...
Be thankful for mopar distributors. You can yank one out, do what you need to do & drop it right back in. Other makes have a bigger challenge.
B.