He's right, and I should have mentioned that but I forgot. Use an FZ in the 1200, but you'll have to replace the top cover plate to accommodate the indentation in the cover of the 1200. That's no big deal as most 1200 floppy drive metal covers will fit on the FZ.
Also, for the 500, you may have to rig up a support bracket to fit the mountings underneath, whereas the big boxes use the side mounts [EDIT: Correction below]. You can use the FB in the 500. Whether you use the FB or the FZ, the 500 cover also has an indentation that you'll have to modify the top of the floppy drive to make fit. The FB that I used doesn't have separate side and top cover plates, it has one big plate with surrounds the drive so I used a dremmel to notch out space for the indentation. (Don't have it on the drive mechanism if you do this, or you're likely to get metal shavings in it. You could also use metal shears.)
Last but not least, I'm pretty sure you must have at least KS2.x in the 500 for it to recognize HD floppies. I have 3.1 in mine, so it works fine. Don't expect a bog standard 1.3 machine to work.
And I don't have another drive to try in the 600, but I would wager you'll have to do the same as with the 1200.
[EDIT:] The 2000 uses the bottom mounts as well. The problem is that the FB cover extends down the sides, then has a side-screw connection to the chassis. You cannot just replace the top cover to make it fit under the hood of the 500, you'll probably have to clip it or dremmel it.
