It's 70s - 80s era? Did they have silencers back then???
Please add:
Stealth Missions, or Options
Moving while crouched (this takes animations... so up to you)
If no moving while crouched, just make stealth disable sound on footsteps or change sound.
Stealth weapons
Knife weapons.
Heavy Rambo Knife.
Flare sounds, I like the PSSSSHHHHHH sound.
Chemlights for stealthy light.
thanks!!