Yes, swapping out one of the floppy drives is really simple. Every Mac SE has an internal SCSI port on the motherboard for an internal HD, you just need a mounting bracket (heck, you could even make one yourself) and a ribbon cable. I suggest testing both of the floppy drives before you make the switch; I've seen a few SEs that only have one good drive.

For the Classic II motherboard, you could make a neat frisbee or coaster out of it