removing the case on a PowerMac 6500/250 tower?

I want to install a larger hard drive in my PowerPC. Unfortunately, I can't figure out how to remove the #@&*! case to get at the drive. I've removed every screw, pried in every direction. There must be a trick of the trade. If you know it, I'd be most grateful if you'd pass it on.

Thanks,
David Engel