Pretty easy- long handled T-15 to remove the two screws under the handle and two at the
lower back. I wouldn't use the screwdriver-you can scar the case and it's usually
not necessary. Put the Mac facedown on a soft surface, lift it a little by the back and
shake- that has always done it for me. Another thing that can work is one of the
"stationary clips" with the round spring (not the ones with the blued spring
steel shaped a bit like a triangular prism).
Once you have the cover off, worm your fingers in and disconnect the power, SCSI, floppy
et al before pulling out the board. The SE&SE/30 expansion cards are two piece, you
should be able to disconnect the cable and remove before pulling the mainboard.