Doc asks:
Would a DSHD floppy drive with a DSHD disk in it
You mean a 96 TPI high-density 5.25" disk and drive (e.g., IBM 1.2M format
that was introduced with the PC/AT)?
look like a 5.25" DSQD drive to an Altos 580?
IOW, could I just plug it in and go?
By DSQD you mean a 96 TPI standard-density double-side drive?
If so, not reliably. You should use a standard-density floppy diskette
in the high-density drive; that should work fine.
Eric