Looking at the period 1965 onwards until the Vietnamese withdrawal from Cambodia in 1989. My interest was piqued by this article that brought Le Duan to my attention:
https://www.nytimes.com/2017/02/14/opinion/who-called-the-shots-in-hanoi.html
Check out Lien-Hang Nguyen’s “Hanoi’s War.”
Obviously she wrote the article, but her previous work selves quite deeply into this subject.
You might also look at Pierre Asselin’s work. He’s an exceptionally gifted historian and an exceedingly nice guy, to boot.