Thanks for these screen captures, @Rob_Nichols! That is a really good catch. These do appear to insert into a slot like a computer video card, or at least that’s how they’re being depicted in the captures above.
Frankly, my intuition is that these served some other function, mainly because of those terminals on the end. Perhaps our resident electrical engineer @dzircher will have an idea. Someone at the MIT Flea Market was selling a huge bin full of these a couple of weeks ago when I was there. They were slightly newer and thus not a precise match for the Cage comm board, but clearly designed to serve the same purpose. They were the same size, had the same terminals, and a bunch of resistors and a small number of transistors. The vendor said she had no idea what they were used for and that she mainly sold them to people using them in Steampunk art.
I actually have a more contemporary practice kit from Elenco at home right now, which is more in line with what I would expect for such a thing: