A cautionary note about use of chatbots like Grok: they are incredibly knowledgeable and amazingly insightful, but similar to humans, they can make mistakes while still being confident. Look at this follow on session I just had with Grok:
Update: I pushed Grok further, and it conceded that the Fairbanks 3-4 was introduced in 1974, not 1973 which foots with my recollection.
As for the surprising (to me) claim that the 3-4 was the base defense for the Dolphins in their first Superbowls, it continues to claim that even after I requested deeper analysis, claiming in particular there was a Sports Illustrated article in 2010 -- still available in their archive -- saying specifically that the Dolphins/Arnsparger used the 3-4 as their base defense on first downs, including in the Washington Superbowl. Grok claims other websites support this.