https://en.wikipedia.org/wiki/KryoFlux

which might let you get most of the bits from a bad block. See

https://goughlui.com/2013/04/21/project-kryoflux-part-1-the-...

The thing I'd recommend is search of an image of the disks if they exist. Next best is an emulation eg [1] [2] which I found by way of google and yandex

[1] https://www.abandonwaredos.com/abandonware-game.php?abandonw... [2] https://archive.org/details/super-solvers-spellbound-dos-en-...

If your goal is to use it on a period-correct system, I’d go with 34/40pin adapters that lets you read flash cards, USB, etc.

A lot of my friends have kept their old 486 computers, and everything is period-correct except for the hard drive and floppy drive which have been replaced with a CF-to-IDE for the HDD and Gotek running FlashFloppy firmware for the 3.5".

I've had quite a lot of success, almost 100%, over quite a long time - both 5.25 and 3.5. I did use older drives intended for "desktop" machines. The drives from Japanese companies seem to be the most reliable; NEC, TEAC. The 3.5 USB Portable diskette drives are based around laptop floppy designs. You won't be able to find a direct 5.25 to USB adapter (or modify one to work) as the speeds / data rates are all wrong, so you will need something like a GreaseWeasel or old PC for those.

I've used different reading mechanisms over the years; an old PC running Linux with a real floppy chipset + custom raw reading code, custom hardware with an F82077 + Atmel + SDCard, and most recently a GreaseWeasel.

The floppies I've recovered were stored relatively well, but were mostly my and family members data - not commercial floppies. If there is any copy protection on the floppies you are trying to read you may need to capture the flux transitions. For these, I'd check archive.org to see if someone has already generated a copy.

For 5.25 floppies fingerprints and surface blemishes can be softened / removed with ISO Propyl and a Q-tip. Floppies designed for cleaning the heads of drives seem to now be very expensive / non-existent. Manually cleaning the heads of a 3.5 drive is way more difficult. I've got ideas about using Face mask / filter material to create a cleaning tool, but it is on the experiments to try list.

Even back when floppies were a thing, I found that 3.5 drives were more un-reliable between machines than 5.25 drives. I think there was more variation in head alignment and track positioning. When I've had issues, I've always been lucky in that switching the drive vendor / model made reading the floppy possible even if it took multiple attempts or was very slow.

Good luck.