They are ATAPI (IDE) based, but around this time their interface wasn't a soild standard - pinouts and dimensions of the drives themselves varied quite a bit. Most ATAPI drives of this era have a custom harness and connector to the motherboard itself. Then again, ATAPI/IDE drives still do have similar issues to this day in terms of dimensions and pinouts (slave/master/CS select also needing checking).

You can replace the drives with the right model (sometimes to a faster model), recalling the stock PB1400 12X drive could be sent in a spin with the installation of a 24X model.

JB