Can you not laser scan the original case for the dimensions? Why make it in aluminium? There are reasons why the Game cube has been (blow) moulded (apart from the expense), machining something like this would be a royal pain in the gluteus maximus mate. If you really are stuck on making it from aluminium then I would suggest 3D printing a dissolvable mould and then casting it rather than machining it. If you use a grade such as LM6 (BS1490) then you shouldn't have any problems. I would strongly advise against using a CNC for this project!