I had quite a few issues with my plus and the Zip, in the end, I made a bootable 44MB SyQuest and that worked perfectly on the first try!

Also my 800k drive doesn't work, I replaced it with a Sony FDHD drive (From a Macintosh IIsi) and now the machine works flawlessly, you still can't read HD disks, but it still boots 400k and 800k floppy's