The SD4 was a very popular race engine. Pontiac in conjunction with Hod Rod Magazine had a magazine called "Pontiac Performance Plus" which detailed building SD4 engines as well as the Fiero IMSA race cars. The SD4 was also used in the 1984 Indy Pace car that actually paced the race.
When GM stopped making the SD4, a company called Kansas Racing Products bought the licensing from GM to continue to make the SD4. It is still used in the ARCA racing series.
http://www.kansasracingproducts.com/Block_Features.html