Regarding 1979 Trans Am with 403 engine What is the rear manifold vacuum outlet connected to?

On a 1979 Pontiac Trans Am with the 403 engine, the rear manifold vacuum outlet is typically connected to the vacuum advance mechanism on the distributor. This provides the vacuum advance signal that adjusts the ignition timing for better fuel efficiency and performance at lower engine speeds. There might also be a connection to the emissions system's vacuum operated components, but the distributor vacuum advance is the primary connection.