AT A1200 floppy troubles

[Stedy]

Was there a little PCB connected to the floppy drive when it was in the external drive?
I suspect there was and this would be needed to make the drive work in your Amiga.

Was it an Amitek drive by any chance?

There are details of the HD floppy hack on Aminet, somewhere.

Good luck

[Stedy]

Some older external floppy drives where directly compatible with the Amiga, most notably the Chinon drives as fitted internally.

You can boot an amiga from the External drive.

These 2 retailers are advertising 2nd user A600 drives which should fit:

16/32 systems & so does Amiga deals

If you are handy with a soldering iron, you could adapt the external floppy connector to an internal one.

Have fun.