My 1988 HP catalog indicates that it is the 9127A 5 1/4" floppy that works
with the 9000/3XX series of computers. For 3 1/2" drives it is the 9122D/S
drive unit that is recommended. There is no mention of an 8" floppy disk
drive for use with the 9000/3XX series of computers
I don't think the older 9885 floppy disk drive would work unless you wanted
to program your own GPIO interface using the 98622A GPIO interface card which
should fit in your 3XX.
The SCSI/HS HP-IB interface is used as a disk drive interface but not for the
9885 floppys.
Paxton
Astoria, OR