I always wondered if that would work out; I've considered making the front half of my black controller red, or something like that. What do you mean by gutting plastic? I assume you had to cut some things inside to make it all fit?
Also, I don't really like the VC stick in place of the control stick. The default left stick in a GCN controller is by far the best I've ever used (in terms of for Smash/GCN, and in controllers in general). I've tried putting the C stick and the CC/nunchuck stick there, neither feel right. The CC stick in particular is way too tall.
First, if you are going to use a official shell with a fake red controller they won't fit sadly, you would probably have to find a black and red controller from the same company to fit and for the gutting part pictures below.
Had to cut (more like pull) out the plastic
That plastic zip tie had to be cut for the controller to close up
And the fake rubber pad (oddly the one from the real control won't let the B button be fully pressed, this one makes the buttons have more click to them but I like it) also in this picture its more clear but notice the gap where the pcb wire goes through, I had to widen it a little, the fake controller's cable is thinner.
Looks pretty cool except it might be nicer with a white stick instead of a black one.
Changed to light blue analog from my nunchuk
, to finish my controller I need the white control for that white wire, so I might buy one soon.