I did it in an Antec case with a Mediator 4000D. My biggest issues were getting the new mounting holes to line up, even after carefully marking them with a fine sharpie through the holes in the board. Just a little off and it's impossible to mount them with the brass stands.
So I used the best holes with brass stands and used plastic ones for the rest as they were a little more flexible.
Second issue was supporting the PCI/Zorro cards. I tore out the case's mountings in the back, since they didn't line up. I used a piece of cutter stick from an industrial paper cutter, which is firm yet soft enough not to crack from the screws, to stabilize the expansion cards.
Of course the bane of these cases is the drive cover, which is prone to breaking off, even if you're reasonably careful with the machine.
