I've modeled the infrared temperature sensor, placed in the nose cavity, and did this rendering to get a sense for how visible it would be. 3D printing is a prototyping technology, but 3D rendering is a prototype for a prototype!
Getting back to it after vacation. Sculpted the temples outward to make space for the mask. Probably need to go back and inflate the mask model by a few mm to make sure there's a thick enough envelope around it - but this is good progress.
I've got the Monster M4sk roughly modeled and placed about where it needs to go. This render shows how I'll need to change the shape of the skull to allow the mask board to be fully enclosed, and probably also change the shape of the eye sockets to fit around the LCDs a bit more evenly.
Figured out how to make a cable compatible with Adafruit's STEMMA port - I2C over a 4-pin JST-PH socket. I would have bought it from them, but they were out of stock, so I bought the crimp sockets and housings from Digi-Key. Crimping them turned out to be pretty simple; the pliers I already had worked great.
Tonight I tweaked the eye bitmaps to remove a slightly-visible ring around the eyeball. I think it's perfect now. Moving on to setting up so I can customize the code running on the mask, to add more features: pulsing the brightness, and then scaling the brightness and directing the eyes based on readings from the infrared sensor.