Some links I have used for the Viet War Pack :
Maps of Vietnam
Vietnam era helicopters
Sitrep and AAR, may be useful as briefieng model
US Army Helicopter Weapon Systems
Air Mobility 1961-1971
Field Artillery 1954-1973
I have also in PDF (From original documents) :
Vietnam Area Handbook
NVA Infantry Tactics
PLAF/PLAVN Tactics, small Unit Operations
PLAF/PLAVN Reconnaissance Tactics and Techniques
PAVN Artillery (Rocket Units)
The impact of the sapper on the Viet-Nam War
The PLAF/PAVN sapper units
VC Infantry Company Tactics
And I can search in a lot of books for specific questions (Osprey...)
Best regards,
Laurent Touchard