Here’s a great documentary on the birth of the Z car. It’s a 1995 documentary, and has very much a US-centric focus, but since the US demand was largely responsible for the success of the 240Z, this is hardly a criticism (although I can almost feel the incandescent rage that diehard Z fans will feel about Count Albrecht Goertz getting yet another undeserved credit for styling the car)
It covers the early history of Datsun in the USA market, and the conditions that led to the introduction of the 240Z in 1969. It also contains great racing footage of the BRE 240Z and later IMSA 280ZX race cars too. It’s rather imaginitively recorded, but well worth the 30mins!