The issue with Dells, even if they're ATX is the front I/O header is on a gang plug, and also things like ambient temperature sensors, and the 4 LED diagnostic panel are there also. Some it needs to run, others you might do without. But Dell doesn't publish the pinouts for these things. So your on your own figuring out how to connect everything. USB, sound in/out, temperature sensor, HDD light, Network light, 4 LED panel are all things I would expect to find there.
Unless you know that 2 Dells are closely related it's usually best to take them or leave them as they are.