Acorn DFS disks are pretty standard FM encoded IBM scheme disks, with 256-sectors and 0-based sector identifiers. There’s nothing particularly special here.
DFS disks are all single sided, but allow the other side of the disk to be
used as another drive. FluxEngine supports these; read one side at a time
-s :s=0 or
DFS comes in two varieties, 40 track and 80 track. These should both work.
For 40 track you’ll want
-s :t=0-79x2. Some rare disks are both at the same
time. FluxEngine can read these.
You should end up with an
dfs.img of the appropriate size for your disk