What colour film was used, I imagine depended on what side of the conflict the photographer was on.
I recall seeing many colour photos in Life magazine, so I can assume that the photographer was on the USA side and therefore used western film like Ektachrome.
I don't remember seeing any colour images from the Viet Cong side and if there were any I would assume they were Orwocolor/Svema type film.
The OP wants to create that colour film look from that period. I don't think Kodak or Fuji films, colour negative or transparency, will recreate that look.
Of course the easiest way to do so in a software programme like Photoshop.
Maybe have a look at some of the Lomography colour negative films. Check out their samples photos on their site and see what catches your eye.
LomoChrome Metropolis colour negative is one example.
LomoChrome Purple colour negative another example.
You could also try some of the "new" Silberra film.
AFAIK, the Lomography Colour Negative 100, 400, 800 are Kodak films and I don't think they will give you the look you are after.
I think shooting in 35mm would better suit your project.
If you do proceed, can we see some of your results, please?