He wrote at least five juvenile books. Not to be confused with the much younger British soccer fan/author.

https://www.google.com/search?q=%22cliff+green%22+books&biw=1152&bih=618&source=lnms&tbm=isch&sa=X&ei=OSqDVMq9MLSOsQSswIDoCg&ved=0CAYQ_AUoAQ#imgdii=_
(book covers - some books are by the other Cliff Green)

https://groups.google.com/g/rec.arts.books.childrens/c/E0RAwWN99DY/m/pH-Nw8djXzUJ
(birthday post from 2014, with filmography and booklist)

https://www.if.com.au/vale-cliff-green-esteemed-screenwriter/

First half of obituary:

One of Australia’s most distinguished screenwriters, Cliff Green (Picnic At Hanging Rock) died on Friday following a long illness. He was 85. Here, Mac Gudgeon and Roger Simpson pay tribute to his life and career.

Cliff Green was a pioneer in Australian screenwriting and a central figure in the Australian Writers’ Guild’s (AWG) early development. His television credits include his celebrated quartet, Marion, inspired by his time as a school teacher in the Mallee, and the sprawling adaptations, Power Without Glory and I Can Jump Puddles. His screenplay for Peter Weir’s Picnic At Hanging Rock remains a landmark in Australia’s film renaissance of the 1970s.

Though one of Australia’s most sought-after writers, Cliff never hesitated to give his time to the guild in an era when the organisation, with only two full-time employees, depended entirely on the efforts of its members and the leadership of its most prominent practitioners. As the force behind the guild’s first national conference, Cliff’s reforms led to state representation, encouraging the spread of membership beyond Sydney and Melbourne. As a delegate to the Affiliation Of English Speaking Writers Guilds, Cliff applied lessons learned in the UK and America to how the AWG operated here.

Former AWG president and vice president Mac Gudgeon recalls: “I first sighted Cliff at a particularly rambunctious guild meeting in the 1980s. Of course I knew of him, how could I not? His writing had entertained and moved my family and I through the adolescent years of Australian television drama. Marion, Matlock, Homicide, Power Without Glory, I Can Jump Puddles, Boy Soldiers were just the start. He seemed to be able to write any genre and his early working years as a country school teacher and his love for Australian writers, especially Henry Lawson, and our vernacular, gave the myriad of characters he created over decades of writing an authenticity, be they male, female, bushie or city-slicker. But his humanitarian heart was always with the downtrodden and powerless, be they poor Irish Catholics in the slums of Collingwood in Power Without Glory or the Boy Soldiers of the First World War. Cliff was a strong believer in strength in unity.”...

(snip)

https://www.newsbreak.com/news/2121148193698/australian-screen-legend-cliff-green-dies-aged-85-writer-of-picnic-at-hanging-rock-the-flying-doctors-and-blue-heelers-passes-away-following-a-long-illness
(includes poster from "Picnic at Hanging Rock")