You can't tell MFM from RLL or any other kind of modulation/coding by looking -- the particular modulation method is decoupled from the interface. For example, many SCSI drives used MFM, as did many IDE drives.

IIRC, the GCC Hyperdrive used an IDE drive (more correctly, ST-506, which became IDE), but with a goofy connector. I am not sure of this, however -- it's just been too many years since I opened one up. Mine was given to me by a friend who worked at GCC. I should've paid more attention to what he told me about the drive details.