Well, ultimately anyone can choose to use any case. All scans on this site can be resized by the individual user and applied to any case, so I'm not fussed if everything goes in as the Universal Game Case.
An 8 or 6 pack DVD case has the following dimensions:
5 5/16" x 7 1/2" x 1" in the old scale (well, here at least - I was 2 years old when we went metric, but still know my miles, chains, yards, links, feet and inches).
So, for an insert I simply added 50 pixels to the vertical of the UGC. So the sleave insert is 3366x2150 pixels.
The photos below are the result. Note that no cutting is required. Also, by great coincidence, the hinges of the middle portions that one simple pulls out are 1/32" wider than the hieght of an NES cart. Thjis holds the cart vertically, which means it doesn't rattle around at all. A perfect fit.
Were can these be bought? Everywhere here, and they are made in China and exported to the world. If and when I get some UGC's, I will be savouring them and wont be cutting them. If you live in the US, I can see an alternative argument.
My dimensions are very rough at this stage. I just wanted to see if slight stretching a UGC sleeve vertically would suit my purpose. It does. The spine may actually be 28mm and not 25.4mm (1").