|"its a simple set of clamps and 4 screws"|
All you need to do is look at the rear of a standard ATX case, then look at the rear of your case to see the differences. An ATX case has the I/O (input/output) ports on the left side, your case has them on the right.
Dell didn't even conform to the BTX form factor with their design. They took the BTX setup & flipped it upside down. With a BTX system the power supply is supposed to be mounted on the bottom.
So even if you were to find a case that you could swap your Dell hardware into, it would be a one shot deal. You would never be able to use it for another system again because no one else uses that layout. You will have wasted who knows how much (maybe $50-100) on a case that has no future useability.