Swapping components SE & SE/30

The difference is the logic board, some slight differences in the chassis, the front case part, swapping the floppy drive to a 1.44MB drive if it was originally a SE with 1 or 2 800K drives. The back case is functionally identical, just a different label on it. The analog board, PSU, CRT and CRT neck board are the same. I don't know about the Classic or Classic II, but the 128K through SE/30 all use the same CRT.

There can be a difference in chassis. The SE/30 chassis has a cutout right above the PDS slot, while the SE, specially non FDHF models, don‘t have that cutout. Still, an SE/30 logic board will fit in, but you can‘t plug in expansion cards in the PDS slot. I have an SE FDHD that has this cutout, so maybe when de SE/30 got in production, they started to make only one chassis and used in both SE and SE/30. There are more little differences, but not ones that can cause problems.