Funny how they later added 'judicial oversight' and things didn't change much. Secret courts are not proper oversight. The FBI should be handling all domestic cases, period (NSLs are another matter).
That said, automated keyword search at that volume in the 1960s is extremely impressive.
This is probably the 1990s-2000s equivalent of doing keyword search for every single 'foreign' phone call coming into the US or across pipes the US controls (one side or both having some international signal). Considering one of the first NSA technology releases was around voice parsing this is likely old hat by now.