I also have an NES. He didn't have any objections to that, and he told me that he wants my outer shell because his is yellow.
I really can't decide between my NES and my SNES. Both are in relatively good working condition, though they both sometimes won't load games if I jam them in too far. I have all of the right equipment to saw off parts of the circuit boards, drill holes, solder, or anything else. I think using the SNES would be more challenging because I'd probably have to relocate the cartridge slot because of its vertical orientation, but I can do that no problem. However, it is a lot of extra work.
Making a game system out of a toaster would really free up space on my desk, and it would look really retro. I was thinking cutting up the outer shell of my NES and using that as a guide for the cartridge slot, but I could also use the guide that's built into the NES, trim the edges off of it, and epoxy or gorilla glue it together. I was also thinking of using some spare cassette tapes as a guide instead.
EDIT:
I just got my toaster and gutted it out. You wouldn't believe how crummy it was inside! I still need to deal with the massive amount of surface rust on the inside. The NES will be an easy fit; no need to trim it down. I'm going to position it horizontally inside the case and reposition the cartridge slot. I have space to jam in a SNES as well, but the slots aren't long enough to fit North American SNES carts. Enjoy some thumbnails. Click on them to see a larger image.








I laughed when I read what it said on the very bottom: "PULL OUT WALL PLUG BEFORE OPENING THIS COVER"
I pulled it out, just not in a way you'd expect.












