I have also added buttons external USB. Why is external USB that so important to many of you?
Finally used the leftovers from the Clone I was using to put it inside one of the controllers.
Now I got a ZNES instead, Zuper Neat Enterntainment Sytem.
So thanks to Nintendo for not wanting my money, this is so much better!
Hope someone finds this usefull, and hey I'm sorry for the Swenglish.
First video, how to fit the Raspberry Pi
https://www.youtube.com/watch?v=-P6FOlKBK_Y
Video nr 2, how to connect working on/off buttons.
https://youtu.be/X74n1htbdmU
Nr, tips on how to add external USB...
https://youtu.be/AbokQ5On3a4
Extra: added the internals from the Clone to a controller.
https://www.youtube.com/watch?v=qvlCs1Ht6jA