5.25" floppies won't mount
By default, the floppy
kernel module is not loaded. To load the module, invoke
sudo modprobe -v floppy
Remember to add your user to the "floppy" group; to do that use
sudo adduser $USER floppy
After the module is loaded you should be able to access the hardware and mount floppies.
I did some research about Varian files, and I came up with this. Said something about a custom 5 1/4" format for disks, customized BIOS routines - I skimmed it. Sounds like it runs from DOS, so maybe it'll work from DOSBOX? Here you go:
http://nmr.tamu.edu/vhelper.php
Re-reading it a bit, the last class of computer that they say it reliably works with is a 486 and almost not at all with Windows. If all else fails, at least you have some EXEs you can work backwards from to potentially determine the format. Here's hoping there's not a whole lot of BIOS patching going on. If you need to attack the Pascal EXE, you'll want to UnLzExe/Upack/Uncompress it before you toss it into your decompiler. Program files from that era are almost always compressed in some fashion. Good luck.
Older Updates
Got a lot of tips for you here:
Edit: Earned a downvote because the question changed, and I didn't change my answer fast enough. Or it's formatted like crap. Fair enough.
Updated Answer
Did you say those had 13 sectors per track? Wonder what kind of disks those are? Research says that they are likely Apple ][ floppies; I don't believe you can read those with a native IBM PC floppy controller. They could also be C64 or Atari disks
This isn't the one I remember, but it may help you out: http://www.deviceside.com/fc5025.html
Note: It says it cannot help you read "flippy" disks without an Apple/C64/Atari drives.
GNU ddrescue
Oh, I see that you are using ddrescue. Last version I used was 1.14, I can't imagine 1.16 is too different. Remember use -c15 for 5.25 QD, and -c18 for 3.5 HD.
Quick Rip, not using direct access. Log will help you remember that it is all good:
sudo ddrescue -Bv -c15 /dev/fd0 floppy.img floppy.img.log
If the disk has bad spots, skip them. Use log for just hitting bad spots next time
sudo ddrescue -Bndv -c15 /dev/fd0 badfloppy.img badfloppy.img.log
If you need to get down and dirty and work around bad sectors, this splits and retries 5 times.
sudo ddrescue -Bd -c15 -r5 /dev/fd0 bf2.img bf2.img.log
Mounting images
That is something I can answer!
To (hopefully) determine fs type:
file -Ls floppy.img
OR
file -Ls /dev/fd0
Now, once you can mount it loopback.
mount -t msdos -o loop floppy.img /mnt/floppy
If it does manage to be one of those pesky HPFS disks, you may be able to use fdisk to determine the offset to mount the hpfs partition, because what you can initially see is just the HPFS FAT-equivalent. I've used it for hard disks before, it shouldn't be that different. Update your question, and I'll return and (hopefully) answer it.
If they're in DOS format, you probably want to use the tools from the mtools package rather than trying to mount it.
Install the mtools package from the archive, and then use "mdir", "mcopy", etc. to access the files.