I had an old thinkpad usb 3.5 floppy disk drive accessory I kept around to boot cranky systems back in the day, as oddly when some wouldn't work with certain usb cd, that floppy always worked. I'd offer it up, but I haven't seen/used it in 10+ years, and don't even know where to start looking for it, but I'm sure you can still find them on ebay.
Good luck on the 5 inch, that you're just going to need an old relic system for I think, but wouldn't surprise me to see some hackers have made adapters to a more modern interface and power for those as well.
-mb