Back in the days (1995 or so) I had my A2000 converted into a bog-standard AT-bigtower, by doing half the Bomac-trick. I simply cut of of the backside of another A2000-case i had lying around and screwd it where the sun should never shine :-D
Converting the AT-PSU was also rather easy (by using the cable from a dead A2000-PSU) and only required some soldering and changing the tick-jumper.
AFAIR the case had 5 5.25 and 2 3.5 drive-bays, and I blocked one of each with accel-card.
So my advice, stay away from ATX, rather go dumpster diving for anything AT big enough.
