IIRC the problem with Dells was the PSU not being 100% ATX - though it used the same connector - it wasn't wired in the standard way, and would nicely go bang if you connected a standard PSU/mobo.

Even with that in mind - it shouldn't be a problem to just move the PSU as well. Watch for the Dell Heatsink/Duct thing - you may have to buy a new HSF