Trying to setup Vive / VRTK in a legacy pre-VR project

As a total noob I’ve been playing with HTC Vive and VRTK (Virtual Reality Tool Kit) and wow, amazing how quick the setup is! Their (his?) tutorial vids are super clear and as such I’ve managed to set up a simple project & scenes using assets ported from an old pre-VR project. Works great! However, ideally I would run the VRTK setup in that original older project/scene so I wouldn’t have to bother with reimporting and placing a bunch of assets. Once I’ve set up the VRTK assets in this old project/scene, for whatever reason, the scene won’t recognize that Vive hardware is attached, while the other fresh scene I’ve created will. I’ve deleted my original FP Camera and Character Hierarchies in the older setup, but still not able to play the scene. Wondering if anyone has had similar experience and tips, or could point me to a tutorial specific to setting up Vive in a project/scene that was not originally built for a VR experience.

BTW, though the project is old, I’m running it in latest Unity v5.6.2. and don’t have any compiler errors to speak of.

Just playing the devil’s advocate here, did you import SteamVR?