Well, I have good news and bad news.
The good news is that have attached my Vive Facial Tracker to my Valve Index VR headset, set it up, and got it working! The bracket I ordered arrived last week via FedEx from Japan (here’s the page I ordered from, although by now you I suspect you should be able to find several other models of brackets via the internet!), and last night I put it all together. Here’s what it looks like:

The bad news? Well, it started even before I installed the Vive Facial Tracker, when I took my weeklong course in content creation in NeosVR, taught by sirkitree and Medra (highly recommended, by the way). I kept crashing out of the classroom, and Medra finally set up a private tutorial session with me in my home world, which worked fine.
But, ever since I set up the facial tracker, I have been unable to stay in NeosVR for longer than ten minutes before crashing out! It would appear that I am bumping up against the limits of the CPU and GPU on my high-end gaming computer, which I bought four years ago.
I will be reaching out to NeosVR for support, and perhaps we can troubleshoot the issue. I did turn my refresh rate down from 120Hz to 90Hz, which is supposed to help with any GPU strain, but I am still stuttering and crashing. Unfortunately, I was thus far been unable to take pictures or video of my avatar in a mirror in NeosVR, but if I succeed, I will share them here with an update to this blogpost!
It is disappointing, but frankly I knew that at some point, for some app, I would reach the upper limits of what my PC is capable. So perhaps it’s time for Ryan to start shopping for a new computer (I already have the store picked out, the same place I bought this computer, which has a stellar reputation for both sales and support). In the meantime, I will keep testing.
Keep your fingers crossed and wish me luck!
UPDATE April 22nd, 2021: It would appear that, alas, the CPU on the computer I bought four years ago is the bottleneck here. Apparently, both Neos and the Vive Facial Tracker are very CPU intensive, and even though I have a good graphics card (a NVIDIA GeForce GTX1080), I will probably have to either upgrade my CPU and add more memory, or simply trade up to a newer, faster, more powerful computer.
I’d like to thank the staff at NeosVR (especially Shift, their Quality Control Lead), and the ever-helpful community on the Neos Discord server for all their assistance in troubleshooting. Thanks, guys! For now, I will be packing my Vive Facial Tracker and its Japanese bracket (which is, thankfully, detachable) and stowing it away until I can upgrade my PC. *sigh*