What’s the story behind these comically large coins?

Trivia type
Mystery object

On February 14th 1966 Australia abandoned the old English system in favour of decimal currency. These props were used in a training video to help people prepare for the changeover.

It was big news in the media, with articles about the design of the coins, the secret of how they were distributed, and this curious piece which described the bronze one and two-cent coins as the "workhorses" and the fifty-cent coin as "the glamour piece".