I'll keep the post in the style of the "BLUFOR versus REDFOR" pairs that the DLC presentations are written in:
Main battle tanks: M48 Patton versus T-34/T-54
Armored Personnel Carriers: M131 versus BTR-50
Fast transport vehicles: N/A versus GAZ-67 (already have M131 for BLUFOR)
Helicopters: Mi-8 versus CH-47 Chinook
Aircraft: N/A versus MIG-21/MIG-19 (already have F4 for BLUFOR)
Additional stuff:
A-1 Skyraider (people forget not all planes were jets - props were still used even in the Vietnam War!)
C-47 + AC-47 "Spooky" (vehicle-in-vehicle transport for C-47 could really help out ACAV! Plus, who doesn't love a good ol' gunship?)
Mi-24 (I know, I know, the PAVN never had these, but super sekrit Ruski documents show Spetznaz GRU was active in Vietnam and even attacked American bases - maybe they decided to bring one with them?)
SR-71 / U2 (haha just kidding... unless? 😏)
Also, despite what seems like a huge headache to implement, I think flamethrowers would be a great addition! Both handheld (M2) and attached to vehicles (M67 "Zippo" and M132). Also the M202 Flash with Napalm rounds!