My thoughts were to reboot this in the UNTAC world.
Usually my stories I start with the boring bit and then get onto the exciting bits later on. However with this reimagining I am writing the border skrimish between Thailand and Cambodia first and then will draft a TL explaining how everything happened afterwards.
My brainstorming thread is here:
https://www.alternatehistory.com/discussion/showthread.php?t=280642
Alternatively when I have considered rebooting Angkor Resurgent I thought about picking up from 1945 and there are gradual butterflies. Now with these butterflies fluttering effortlessly across Vietnam, there is widespread independence in the former Indochinese colonies and Vietnam is united under Ho Chi Minh.
The second alternative would be Mr Sisowath assumes the throne in 1966 as the war in Vietnam is heating up. Cambodia has limited options, a declining economy and a miniscule military. I think the term was an ant stuck between feuding elephants, so he has nine years to strengthen the state in order to defend against the communists in 1975.
As an aside King Sisowath remains my favourite character from all of my TL's thus far. Accordingly I have always wanted to continue his journey. So preferences?