Well, I don't know nothing about that nam units, cus I never played any nam mission, so I don't have any nam addons. I'm not sure if I can help you about this, but if those choppers use the "standard" weapondry, try this:
<unitname> removeWeapon "HellfireLauncher<choppermark>" for homing missilies,
and "MachineGun30" for the mgun.
If this not work, then look in the addon readme, the authors usually write there the weapons and the ammo names, and replace those names that I gave you with that readme (original) names.