1. In 70, the original firewall tooling for the 70 E-bodies had no dimples 2. In 70/71 as California cars required the Nox device, the firewall tooling was revised with the dimples 3. In 71, cars being sold in California had the firewall dimples punched out to accomodate the Nox device 4. In 72, when all states required the Nox device all firewalls had the 3 holes punched out
