Most tachs were dealer installed Dixco tachs with a licensed Chevy Bow Tie. They were mounted on the column angled down about forty five degrees and held in place with a screw type stainless steel hose clamp.
Dixco and Sun were amongst the first electronic tachometers made. In 1964 Chevy was still using a mechanical tach driven off the distributor as electronic (transistors had just recently been unintentionally declassified by the Japanese who had copied the transistorized circuits found in Lockheed's F-104 Starfighter jets stationed in Japan). Transistors had been a military secret up until Japanese transistor radios suddenly appeared on the market.
To Quote Gomer Pyle USMC "Surprise, Surprise, Surprise!" If you have ever read Sun Tzu's book "The Art of War" you would understand how our ally could treat us this way, and why we should not have forgotten what happened at Pearl Harbor. But that is history for you.