as I have done some work with IIcx's and IIci's (same enclosure, I think) let us see:
This plastic tray with the HD and the floppy on it has a kind of half tube running down vertically to the center of the motherboard.
There is a screw at the bottom of this tube. Also, you have to take out the power supply and then you can bend the plastic tongues a little (near the alteral wall of the case) and take out the whole tray (after you have removed the hard disk, of course).
Hope this helps,