SI is an acronym for systems integrated because the voltage regulator was moved inside the alternator. GM built millions of these units from the '70s until the CS130 debuted in 1986.

1987-1994 Delco-Remy CS-130 GM alternator adds more power using National Quick Start's Iceberg alternator upgrade - 4 Wheel and Offroad Magazine ...

Most one-wire alternators are an upgrade of the GM/Delco style unit, and you can get a conversion harness to run a charge light on the dash.