Dell's are proprietary.  Its possible to move it to an ATX case but the front panel connects are proprietary and undocumented so unless someone has traced out what wires are what its up to you to figure it out.  Dell also uses proprietary case fans that the BIOS must see or you will get a fan failure notice at power on and have to press an F Key to continue the boot.  There are some adapter cables available to connect standard fans to the Dell fan headers. I can't say about your antenna problem.  
Help! I have a Dell inspirion 3671, it’s a good computer, but I decided it was time for a graphics upgrade. Alas, the graphics card I bough didn’t fit within the current case so I decided it was time for a case upgrade. I bought the NZXT h510. Only problem, is that there WiFi/Bluetooth card seems to have antennas that connect to metal pieces on the outside of the case and it’s impossible to get them out without cutting them. Is it even possible to recase this pc? And how do I fix this problem with the WiFi/Bluetooth card?
New case for inspirion 3671