Building cases

I have some eclectic but fairly worthless side tables and furniture that would make very interesting and unusual PC cases. I have a 1930's record player cabinet with matching record storage cabinet 6' long. Both would make cool dual PC's. Take the speakers out and put in a round window or fish bowl. What I need is the back of a PC case the back 1 1/2 to 3/4 of an inch of the case and the I/O plate and shield. Just like someone had cut the back of a case off. I need it several sizes compensating for the woods thickness.
Anyone know if they are made by someone already? Or which case company would most likely help to see if a customer's idea works as a new product. Making these to sell to people would work. Only need 4 different sizes for mounting in just about anything. Just think of all the things you could mount a PC in, super easy if these were available. Lian Lee makes something close but it's missing the sides to be able to mount it to the cabinet. I thought of cutting a cheap case but they don't come in the right shape or enough slots or big enough. They are welded to frame parts or no strength left after it's cut. Anyone have any ideas? Thanks.