I have an SE that is different from my SE FDHD and SE30 metalwise. The SE FDHD is pretty much the same as the SE/30 inside, the slot where the PDS card would go is the same and the riser where you would screw an ethernet card input is screwed to the sheetmetal. On the SE the bracket for holding the network is spot welded, and the PDS slot is different in length. The motherboard also seems much tighter to the sheetmetal, so a SE30 MB would probably not fit because of the SIMMS sticking out too far.

The SE top floppy opening on mine is closed and hole where the HD led shines through, thic can be removed if you want to do a 2nd internal floppy.