Aside from leaving the side panel off, not much. I wouldn't expect too much overheating, their rear case fan should be enough to handle it. As long as the front of the case has a clear path to cool air, it should work. Makes for a pretty dusty PC, but that is typical of OEM builds.
Really transplanting a motherboard from one case to another is not that difficult. Worst problem might be the front panel connectors since Dell tends towards customization there, but places like moddiy.com sell adapters.
1) Remove side panels
2) Unplug data and power cables, note the order the data cables for the drive(s) are plugged in (if applicable)
3) Remove expansion cards
4) Remove drives
5) unscrew motherboard, remove
6) remove I/O shield from the chassis
7) Remove power supply
8) install power supply in new chassis (or install a new power supply, or use an included one)
9) install I/O shield in new chassis
10) install motherboard
11) plug in front panel connectors (from chassis to motherboard USB, power/reset switch, activity lights)
12) Install drives
11) Plug in drive power and data cables
12) Install expansion cards (plug in power if applicable)
Plenty of YouTube videos for how to build a computer, and you can certainly put in more specific terms. But this would mean no OS installation, CPU installation, heatsink installation, memory installlation. That board can come out as is.