[Jeff Lee]

The 383 / 280 engine is the non-magnum engine; smaller cam than the 383 Magnum engine. Might even be a slight decrease in compression, check the specs. As used in the '67 A-Body cars, it also suffered from a very restrictive cast iron exhaust manifold.
The WB has nothing to do with anything. But sometimes it is a reflection on what is being run in competition and subsequently it may be hit by the AHFS.