Updates
It's inplace!
I used a jiggsaw and my dad to help with the cutting. After that I used the file Dan provided to even it out, then sanded it down till it fit.
The top and inside the sides are somewhat scratched, but I'm going to remove them with some Wet/Dry paper at different gradients, then use some Brasso and silver polish to put it back good as new.
It's also sealed, and I went a different way of mounting it. This time instead of nails, I used a small shelf type system, which adds a slightly more futureistic look to the cube because of it's metal grounds that hold it to the cube.
Pictures
here.