Just to recap:
Hard disk: you install FFS into the MBR and it then works with just about any OS as long as the controller understands RDB. It may be that if you use the FFS from 3.1, it'll crash under 1.3, so if you have a disk you intend to use with both OSes, try it first and if it doesn't work, then install the 1.3 FFS onto the RDB.. (you lose international mode and don't even think of using over 4GB disks/2GB partitions with the 1.3 FFS)
Floppy disk: OSes from 2.0 forwards know FFS floppies without any tricks, but with 1.3 you need to create and mount a separate device to be able to read FFS (and also no booting from FFS floppies).
It's rather simple - take a look at your devs:mountlist when you've booted to wb1.3, there's a device called DF1: and a device called FAST: .. make a new device called FF0:, and combine the DF1: stuff (change unit to 0!), and get dostype and filesystem from FAST: .. then do a mount ff0: in a cli and you can use ffs disks in drive df0: (they show up inside the device ff0:)
Don't be alarmed by the above instructions, you'll understand it the minute you look at the mountlist..
Perhaps you need to issue a diskchange ff0: after you swap disks, I'm not sure as I haven't played around with 1.3 for ages.. And I'm too lazy to try it now. I'll leave some joy of discovery to you.
