They definitely go back earlier than early 70s, but not sure how far back.
Ford Australia used Cibie Oscars on the London to Sydney Rally cars in 1968.
Here’s KAG-002 (placed 3rd outright). Note the Oscars....
I'm assuming Oscars had been available for some time before that, so they are probably at least 'almost' period-correct
Cheers,
Glen