I have a Dell Optiplex, an older model than yours, but the case is the same. I wanted to do what you want to do because whilst the computer is cheap the small form factor case makes it difficult to bung a decent graphics card or other upgrades in. Anyway I took it all apart and offered it up to my bigger box and found that the rear plugs and sockets are not in a standard position to fit a standard box without carving up the case to make everything fit so it all went back into the Optiplex case. I don't know whether there will be a non-standard normal sized case that your MB will fit into. I didn't go down that road I fitted normal sized graphics board and a USB daughter board and made a bracket that would give the boards support and left the side of the case off. My computer is in a cupboard so aesthetically it didn't matter.