I have put an N64 into a Gamecube Gameboy Player. I modified the console so it runs off the Gamecubes Power and audio/video cables.
I coupled it with a Everdrive 64 so I can play N64 games off an Sd card.
I added this to my Gamecube that already was modded with a WiiKey Fusion that plays games off an Sd card.
http://www.youtube.com/watch?v=Z0VY-wJc77A
I had to :
1. Remove the Gameboy Players internals and remove a lot of extra plastic.
2. Trim the N64 main Board down to fit.
3. Trim and fold an Expansion Pak.
4. Trim and fold the Cart slot and rewire it.
5. Move and re-attach the 4 controller ports
6. Add an external reset switch.
7. Added vga ram heatsinks.
Here is the thread at the Modretro forums :
http://forums.modretro.com/viewtopic.php?f=3&t=11029&p=142397#p142397