The tape hack is a bit of a hit-or-miss affair. It works best if the disk has *never* been formatted as 1.4MB (or if it has otherwise been erased with a degausser). The write field of an 800K drive is a bit on the low side, relative to that in a 1.4MB drive, so an 800K drive may not reliably overwrite any data previously written by a 1.4MB drive. Add a small amount of track misalignment between drives, and you can quickly eat up any margin that might have existed. Even if things seem to work, that may be a temporary state of affairs. The tape trick should therefore be reserved for emergencies.

Since the media used in 720K PC disks is exactly the same as that for 800K disks, just hunt down some of those. It's a lot easier, and you'll have much less trouble. Many office supply stores have stopped stocking them on their shelves, but will happily order them from their warehouse for you. And there are still many online stores that stock them cheaply.

Too bad you don't live near silicon valley. I've got about a trillion of these I'd happily give you.