Why not just download the .sit.bin file on the PC, put it on a floppy, and then open it with StuffIt 5.5 on the Classic II? That should work. If you don't have PC Exchange (for reading PC floppies) on the Mac (not sure if an OS as old as that has it), then you'll need to format the floppy in the Classic II, and use TransMac for Windows to move the .sit.bin across to the floppy. That should convert it to just .sit, and then you can open it with StuffIt on the Mac. StuffIt should also open .sit.bin - you'll probably need to open StuffIt and open the file from there, rather than just double-clicking the file.
