Finally got around to setting up that adapter for using a GameCube controller with an N64.

The source and schematics for the project I used are here: https://github.com/brownan/Gamecube-N64-Controller

brownan/Gamecube-N64-Controller

Gamecube-N64-Controller - Connect a Gamecube controller to a Nintendo 64 using only an Arduino and a single resistor