Did you try Shrinkwrap?

I was making backup images of every disk I have such as important ones, like the System 6 Emergency Network Access Disk. Shrinkwrap would image it fine, but Disk Copy would fail to copy it properly.

I also found my SE/30 didn't like the 7.5NAD produced by Apple by the $ dd command. Makes backup and recovery hairy, as OS X adds things to a floppy like .Trash and other non-target relevant data which robs space.