The original SE (4 SIMMs are angled) doesn't have much clearance for the motherboard, a SE30 with the 8 SIMM slots (that stick straight out) will not fit. The difference between a SE and SE FDHD is a chip swap I think for the floppy controller.

I have a SE 800K (1 floppy and 1 HD) and a SE FDHD (dual 1.44MB floppies), they are nice machines for a 68000. My SE case is trashed, but other then that it runs fine.