Hi!
I think you can't boot from df1: if you have Kickstart ROM 1.2 or 1.3.
You must have ROM 2.04 or newer in your machine to be able to select booting volume.
But I would try to open the case of Amiga and also open that external drive case, so you can connect internal drive cable to it and don't forget to set jumper on that external drive to df0: setting.
Hope it will boot!
