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You would want something like this. The important part is that it comes in two pieces so you can install it without having to disconnect anything to pass it through. The brushes are to resist airflow, but they are obviously not going to be airtight or pest resistant. For that, I would use expanding foam insulation. Those cables and pipes aren’t going anywhere, and if you absolutely had to replace one, removing the sprayfoam is a trivial effort compared to the rest of the job.
Ooh, I remember playing Monster Maze and Math Hurdler on a dual-sided cassette. Avenger (basically Space Invaders) on cartridge. Also typed in Killer Comet and Tank vs UFO from a magazine. Last one was probably the best of the lot.