Hi JimJagger, great that you've still got your Amiga and it's (mostly) still working! Hours & days of fun are ahead.
I had a similar HD to that one, like Scuzz mine was branded the Archos Overdrive 35. Mine had a separate power supply which plugged into a 3-pin plug but from your description I think your power supply plugs into the floppy drive port (like on Scuzz's pictures?). This doesn't make the hard drive DF1:, it's only using that port to get power.
The way mine worked if I had to boot from floppy (I am trying to remember back about 20 years as I stopped using my Overdrive when I got a Blizzard Accelerator and they don't work together) was a small 'AQ' icon appeared on the Workbench (it's a bit strange - a small icon with no apparent name but it was cleverly blank by it being named a single space). Double-clicking this mounted the partitions which were called AQ0: and AQ1: as standard. You can run this command from shell by typing " " and hitting enter (that's quote-space-quote).
I recall that the Overdrive was very particular about it's set up and the boot partition (AQ0:) must be 8MB and AQ1: uses whatever capacity is left. I still have my boot floppy which has tools on to set up the hard drive in this way (effectively reset to default settings).
Overall the Overdrive is a case and adapter with a standard 3.5" IDE hard disk inside so if you DO need to replace the disk, then it's quite easy to do.
