HEI in a Mopar?

OK, so I've seen this swap mentioned in many threads lately involving troubleshooting of ignition problems, but I must be confused about something...are there aftermarket dizzys with HEI parts in them or are some of you guys retrofitting original parts in series with HEI parts? If so, how is it configured, how much does it cost for basic modification, and what are the advantages/drawbacks?