More info: there's definitely something screwy about that System 1.1 disk image. The real floppy drive magically started working, so I made a 400K floppy from the System 1.1 image, and tried booting the Mac 512K with that. It crashes with the same 0F0062 Sad Mac error as I get when using Floppy Emu, so it's definitely a problem with the software and not the Floppy Emu. Strange that the same System 1.1 disk image boots up fine in a Mac 512Ke and a Mac Plus. But at least the Floppy Emu seems to be behaving identically to a real floppy drive here.