The Australian Jungle Green uniform shown on this page was adopted in 1958, largely based on jungle uniforms used by Commonwealth forces in World War 2. It is sometimes called the “1st Pattern Australian Jungle Uniform” and is much heavier weight than the “pixie uniforms” that replaced it (source: http://www.vietnamgear.com/kit.aspx?kit=707). It appears to be an Australian-made version of the British Pattern 1950 jungle uniform (source: https://talesfromthesupplydepot.blog/2014/12/07/1950-pattern-tropical-trousers/)
Pants:
Tag:
1966 Date.
Thigh Pocket:
Back Pocket:
Waist Adjustment:
Belt passes through waist:
The waist adjustment allows for the waist to be tightened as the wearer lost weight from prolonged fighting in the jungle (source: https://talesfromthesupplydepot.blog/2014/12/07/1950-pattern-tropical-trousers/).
Inside:
Ankles:
Buttons:
Thigh pocket button. 
Fly button is typical British commonwealth dish pan type.
Usage Photos:
Indonesian Confrontation:
1965: Soldiers of the 3rd Battalion, Royal Australian Regiment (3RAR), board a RAF Belvedere helicopter to search for Indonesian infiltrators near Sarawak, Borneo (from https://www.nma.gov.au/defining-moments/resources/indonesian-confrontation). 
1960: Soldiers of 1st Battalion, The Royal Australian Regiment (1RAR) in the jungle north of Baling, near the Thai Border (image from https://www.nationaltribune.com.au/honouring-our-veterans-who-served-in-malaya-and-borneo/, caption from https://www.awm.gov.au/collection/C206955).
This jungle uniform is most commonly seen in Indonesian Confrontation photos.
Vietnam War:
Although more modern uniforms were available by the late 1960’s, items in this older cut continued to be used throughout Australia’s and New Zealand’s involvement in the Vietnam War.
Australian Forces:
August 26, 1967: Members of 5 Platoon, B Company, 7th Battalion, The Royal Australian Regiment (7RAR), just north of the village of Phuoc Hai, beside the road leading to Dat Do. United States Army Iroquois helicopters are landing to take them back to Nui Dat after completion of Operation Ulmarra, the cordon and search by 7RAR of the village of Phuoc Hai. Operation Ulmarra was part of Operation Atherton, conducted by 2RAR/NZ (Anzac) (The Anzac Battalion comprising 2nd Battalion, the Royal Australian Regiment (2RAR) and a component from the 1st Battalion, Royal New Zealand Infantry Regiment) and 7RAR (Australian War Memorial photo EKN/67/0130/VN, from https://www.awm.gov.au/collection/C195204). 
Saigon, South Vietnam1968: New Zealander/Australian war correspondent for UPI, Kate Webb talks to troops on the battlefield in South Vietnam in 1968; Webb was captured by North Vietnamese forces during the war and was released after her obituary had been published; (Photo by Nik Wheeler/Corbis via Getty Images, from https://www.flickr.com/photos/13476480@N07/51233959833/in/photostream/)
New Zealand Forces:
From https://www.v4coy.com/vung-tau—saigon—locals.html. 
From https://www.v4coy.com/vung-tau—saigon—locals.html. 
From https://www.v4coy.com/operations-1.html. 
From https://www.v4coy.com/operations-1.html.
From https://www.facebook.com/photo/?fbid=10154446946996926&set=pcb.10154446952596926. 
December 19, 1972: 2NZATTV (2nd New Zealand Army Training Team Vietnam) just before withdrawing from Cam Ranh Bay airfield. The team had been part of the Dong Ba Thin UITG/FANK Training Battalion comprised of US Special Forces officers and NCOs and their Montagnard security company, with the job of training conscript Cambodian infantry battalions airlifted in from Phnom Penh (from https://vietnamwar.govt.nz/photo/2nzattv-departure-svn-19-dec-72).