You could use a netatalk server and a system 7 network access disk. Keep a copy of Disk Copy on either the NAD or the server, and literally take an image of the whole drive every once in a while.

Retrospect may also be able to back up to floppy diskettes, but netatalk is likely to be your best solution.

The gotcha is that you will have to reboot the machine into the network access disk, and use either serial localtalk, a large external hard drive (a scsi2sd perhaps?) or a normal Ethernet connection to talk to the server. If these are things that need to be running 24/7, retrospect or just copying the files with finder will work a little better.