I can't tell you specifically, but I worked with the 6300's for some time back
in the mid 80's. If I remember, they had a generic 10Mb drive, so I would
imagine a Seagate 225 would be about the right generation. The floppies were
black on the units we used, and were also otherwise unremarkable. The floppy
controller I can't comment on, other than I would imagine an ISA controller
would work with them.
As far as I could tell, the 6300 series were essentially an IBM clone minus
the basic. They ran MSDos and PCDos equally well.
Steve Wilson