Okay, then...
Actually, I think you're misunderstanding how BasiliskII/Sheepshaver work on UNIX hosts. (I don't care about Windows, which is what the BasiliskII link is about, so on that you might indeed be up a creek. Too bad, get a real operating system.) It doesn't matter that "Sheepshaver has no SCSI, floppy, or any other external device" support. As long as the *host operating system* has device drivers supporting the disk device in question and is able to present the whole disk and/or individual partitions as readable nodes under the /dev tree Sheepshaver/BasiliskII can use those device nodes for disk access. (The Sheepshaver manual shows it having the same /dev device options as BasiliskII. You set up the nodes as if they're disk images, not as entries under the "SCSCI" tab.) Again, I'll grant all the documentation about this is for Linux, but I'm willing to try it under OS X. Let's see...
(Crunch and waste some time here...)
Yes, it works. I just took a USB key (only "removable drive" I had handy) and used OS X 10.5 to erase it, write a new APM partition table (this is an important thing I had to work out, as when I merely told disk utility to put an HFS standard filesystem on it it retained the DOS MBR partition table.), and format the file system. So my USB key "looks like" a ZIP drive or external hard disk formatted on a Classic Mac. (Connected via, say, a SCSI/Firewire or SCSI/USB bridge.) Then after that, well... there's some kinks to doing this under OS X that aren't there under Linux. Luckily, other people have encountered them before:
First off, since I was using a USB key instead of a hard disk, if I used the GUI to unmount it it'd actually destroy the device node in /dev/. Here's how you get around that using the terminal commands for manipulating volumes. This problem might apply to floppy drives as well.
So after I did "diskutil unmountDisk /dev/disk2", I told Sheepshaver to mount "/dev/disk2" (the root device node for my now unmounted key) as a second volume. I am not the first person to do this under OS X. Here's a guy mounting the hard disk from his dead iMac G3 exactly the same way. I did what he did.
After doing this I booted Sheepshaver, and viola, I can see the HFS filesystem on the key, and I can drag files to and from it. Once I'm done fooling around in Sheepshaver I shut it down and then run "diskutil eject /dev/disk2". Then I pulled the key out and shoved it back into the Mac and viola, I can see the files I wrote to it. Eazy Peasy.
As demonstrated, it does work. Now, as to how useful this is: I will grant that if you just "dd" the entire volume into a disk image, manipulate it, and then write it back out the end result is basically the same. The difference is that if you're doing this to a 120MB ZIP drive you're stuck reading the entire volume into a file (ZIPs aren't fast), and then when you're done writing the entire mess back out again, while if you just mounted the ZIP inside Sheepshaver you can copy your one file and be done. (dd is also an example of one of those "scary" commands that can trash things if you foul up the command line syntax, which is another reason I don't like it, and it also doesn't do any error checking. It just blindly grabs bits and stuffs them out the other end. Mounting a disk as a filesystem *might* be slightly less likely to accumulate errors over repetitive use, although I'm sure you could make a case either way.)
dd'ing *is* probably the correct answer for floppy transfer as apparently Sheepshaver has issues parsing floppy devices directly under OS X, but for shuffling hard-disk-size volumes around, well, maybe not. Both require roughly the same level of "arcane-ity" at the command line.
Anyway, didn't mean to insult you, if you took it that way. Just pointing out there are other alternatives.