@Senpai - Added all 3. Nice work! It's really great to see full game series completed in this cover style. So far I think we now have complete sets for the Donkey Kong Country/64, Mario platformer series, Pokémon and Star Fox games across NES/SNES/N64.
I went with the 2nd method Breakmanexe posted above of modifying an NES case to fit the North American Super Game Boy, and it works pretty well. I don't have a Super Game Boy 2, so I'm not 100% sure, but I would imagine the same modifications might work for that too.
EDIT: Not directly related to ShadowFox cases, but here's a look at a project I never finished. I found this while I was looking through my old photoshop files today. Back in 2016, I toyed with this as a companion cover set to this ShadowFox case template, designed for 8-disc DVD cases. The idea was to house Nintendo-related series and movies; this would be things like the Pokémon anime, Super Mario Super Show/Adventures of Super Mario Bros 3/Super Mario World/SMB The Movie, etc.
I got as far as making this mockup of Pokémon Vol. 1, which it seems would now perfectly house the Indigo League Blu Ray, First Movie Blu Ray or DVD, and Pikachu's Winter Vacation DVD.

I also found a document where I mapped out the volumes:
Pokémon Vol. 1: Indigo League, First Movie, Pikachu's Winter Vacation DVD (8/8 discs)
Pokémon Vol. 2: Orange Islands, Movie 2000, Johto Journeys (8/8 discs)
Pokémon Vol. 3: Movie 3, Johto League Champions, Mewtwo Returns, Movie 4 (8/8 discs)
Pokémon Vol. 4: Master Quest, Movie 5 (8/8 discs)
Super Mario Vol. 1: Super Show V1, Super Show V2 (8/8 discs)
Super Mario Vol. 2: Adventures of SMB 3, Super Mario World, SMB The Movie (6/8 discs)
Not sure if I'll continue to develop this, but I thought you guys might like to see it.