Just in case anybody wants to do this in the future, I've solved it. The issue with having it not move when using G1 Z-999 H1 was my M574 needed to be set as a probe (Z) and I used the Z probe input pins. I had previously been trying the Z probe pins with S1 and the Z endstop pins with S1 (unsure as to why the endstop pins with S1 didn't work.)
At some point I'll show the new probing method...