I'm talking about this sort of voice: https://www.youtube.com/watch?v=nzOH9vIW5J8

It was very common in broadcasting from the 1930s to the 1970s, after which reporters used a more conversational style.

How was it taught and are there specific rules and techniques? I'd really like to know of any references or even any descriptive books about it from that era.

In modern movies in the past 10 years or so I've heard actors trying to recreate these voices, but they don't really sound authentic, so I wonder if information about this style has been lost over the years. Many of the reporters from the 1930s-1960s seem to have the same sort of diction and enunciation, so there had to have been a manual of some kind they worked from.