I would give the usa a save of 6+, as the vests was not that good, most did not wear them, too heavy and hot, so a 6+ is fine...
As for the vc, they need a rule, based on the fact they was well hidden and great at ambushes etc....
SO you can have the trat..
"Jungle fighters" : Trained to fight in the hot jungles, when in cover, they get a save of 5+
"Lay of the land " Obscured always become cover, as they know the best places to hide
T 4+
K 6+
SV X
IN COVER
T 6+
K 8+
SV 5+
Standed North army, could just have the jungle fighters skill, locial fighters can have lay of the land, and the best trained Vet cong can have both...
How does that sound...
Most of the battles will be in Heavy jungle ( cover ) Long glass, or Lt wounds will be Obscured, with open Lz`s and rice fields, the banks of the rice fields can be Obscured as well.
Vetcong will forget the first suppression against then each turn.
Try that and have fun, sorry i cannot give you helicopter rules, until the rulebook comes out...
Alan