This version of the board has big solder pads for drive select 0, 1, and 2. Originally, this was intended for use with a single HxC drive installed into a PC-8801, where you can route the "DS0" pin from the second drive connector into the HxC "DS1" pin to enable dual-drive emulation.
Exposing these pads makes fitting the whole mess inside the case more challenging, so if you do not anticipate that you will need this particular configuration, please use the other release.