Of course I didn't consider the fact that the archive may be split across several disks..or indeed all of them, there probably are ways of coping with that but you would need to know which disks form a set (or if it is one big set made at the same time..which would be very bad)
Of course you could also try some symlinking of device nodes so that your floppy drive appears on a tape device node and see if tar will read them direct...but if this is the only copy of this data then I would be tempted to dd each floppy to a file first anyway because then you can replace any that fail due to disk errors during later attempts.
Regards Wayne