Adding the ARVN doesn't seem like it'll add a lot, but actually, it would open up a lot in terms of vehicles.
After the Americans left, the North Vietnamese began to use lots of tanks and infantry vehicles, particulary in the 1972 and 1975 Offensives.
Not to mention, the ARVN made heavy use of the M113 APC, which would be awesome to add.
https://en.wikipedia.org/wiki/First_Battle_of_Quảng_Trị
https://en.wikipedia.org/wiki/Battle_of_An_Lộc
https://en.wikipedia.org/wiki/Ben_Het_Camp
https://en.wikipedia.org/wiki/1975_Spring_Offensive
https://en.wikipedia.org/wiki/Easter_Offensive
After the Americans left, the North Vietnamese began to use lots of tanks and infantry vehicles, particulary in the 1972 and 1975 Offensives.
Not to mention, the ARVN made heavy use of the M113 APC, which would be awesome to add.
https://en.wikipedia.org/wiki/First_Battle_of_Quảng_Trị
https://en.wikipedia.org/wiki/Battle_of_An_Lộc
https://en.wikipedia.org/wiki/Ben_Het_Camp
https://en.wikipedia.org/wiki/1975_Spring_Offensive
https://en.wikipedia.org/wiki/Easter_Offensive