I'm ogling the tri-color eink display https://www.adafruit.com/product/4128 that goes along with Adafruit's Feather controller. That sounds like a promising lead toward developing this project. From the Adafruit site:
Product Dimensions: 61.3mm x 40.4mm x 6.7mm / 2.4" x 1.6" x 0.3"
So clearly the proportions are off. I'm too lazy to look up or measure the real pager's proportions but it looks wrong. But I'm OK with that. I'm assuming I would be 3D printing the casing at some point, rather than repurposing an original, so ultimately it doesn't matter what the front looks like. (Other than wanting it to look like Cereal Killer's yellow Advisor.