Well, I've found
something of use under Linux. The "dd" command on "/dev/<whatever>" will load/store an image of the drive. So, that does what I want for drives of the same size.
For drives of different sizes AFAIK the cluster size (and perhaps other information) will need changing, something requiring knowledge of FFS. I've found some good docs on Aminet on this but need time to study them to see if it's feasible! :smileek Of course, if the drive image will work on a larger drive without modification that would be fantastic but somehow I suspect this won't be the case...