What are the dimensions of the C64 motherboard? I am specifically asking this because I am considering using a 64C case (these still seem to be in production) for an 8-bit homebrew machine. I wonder if it is possible to design a board in such a way that it would fit the Commodore case as well as a standard something-ATX PC case.
There are several revisions of the C-64 board (see, e.g., here , or here), with two major form factors: the old "long board" and the new "short board". The long board (which I happen to have on my bench right now) is approximately 39cm wide and 18cm long, the short board is just as wide, but a little, well, shorter.
If you need exact dimensions and drill points, you could look at some of the replica PCBs that are floating around on the net, like these, maybe even use the board files as a basis for laying out your PCB.
One thing to keep in mind when designing your own PCB is that, while the long board does fit into a C-64C case, there's not much vertical clearance on the lower end - just barely enough for a socketed DIP IC, so don't place anything tall there.