I picked up a junk original model X68000 the other day. It was really cheap and I reckoned I could use the case if nothing else. Turns out it works perfectly well - a rarity really, when you consider how often the PSUs blow up - except that the floppy drives are dead.
The floppy drives in all X68000 models are the same, with three exceptions. The Compact units have 3.5" drives, the Pro has massive heavy drives with flat ribbon cables instead of the wire clusters that the rest use, and the original X68000 has drives with two subtle changes:
The data cable connects on the opposite side of the mechanism, and there's a secondary 'eject' cable that isn't present on any other drive. It seems to be additional, so that I expect the drives to be still compatible if you don't use this 'eject' button that's present on the rear of the original X68000 (but none of the later models).
The differences in the original model don't end there! The power supply is a separate box not attached to the rear of the system like the L-shaped ones in all the other systems. There's a rear PCB that stacks the SASI + FDD ports on top of instead of beside each other. It also has the FDD eject button on it, which no other system has, and the FDD cable is hardwired to this PCB where in all the other systems it's removable and attached to the PCB in the base of the unit.
On the other side of the system there's some more strangeness. There seems to be a completely separate video board, housing the video chips and all the VRAM. Normally everything but the video input port are on the mainboard, so this is a very un-optimized piece of hardware. There's a lot less shielding than in other units too.
The expansion RAM board shown in the top right corner is custom to this model. The CPU and peripheral controllers are under the cart slots, which is nowhere near where they are in future models.
This system has no extra space inside for additional hardware, like an internal HD. Sharp did amazing work compressing the system down in subsequent revisions of the system.