Is there a notable difference between the two? Would it be worth soldering that header in, you think? And for what it's worth, G30 definitely stopped on setting 4, so that's certainly an inch closer!

I have them on the old Z-Probe pins, which are on the PWM3 header, as seen below. I am only using the pins designated by the arrows:

Included in this followup post, is my config.g and bed.g Do you see anything amiss?

; Configuration file for RADDS 1.5 (firmware version 1.17 to 1.19)
; executed by the firmware on start-up
;
; 

; General preferences
M550 PCyberDelta Plus 2187 V3.0 Championship Edition: Round Deux ; Machine name
M111 S0 ; Debugging off
G21 ; Work in millimetres
G90 ; Send absolute coordinates...
M83 ; ...but relative extruder moves
M555 P2 ; Set firmware compatibility to look like RepRapFirmare
M575 P1 B57600 S1					; Comms parameters for PanelDue

;*** The homed height is deliberately set too high in the following - you will adjust it during calibration.
M665 R116 L288.12 B116 H225.9 X0 Y0; Set delta radius, diagonal rod length, printable radius and homed height, as well as XY tower corrections
M666 X0 Y0 Z0 ; Put your endstop adjustments here, or let auto calibration find them
M208 Z0 S1 ; Set minimum Z

; Endstops/Probing
G31  P100 X0 Y0 Z-0.1     ; Set Z-Probe Height and offsets.
M574 X2 Y2 Z2 E0 S1       ; All endstops at high end, Active high
M558 P5 R0.4 I1 H3 F1000 T1000       ;P = Z-Probe Type, 0 for none. I = inversion XYZ = use probe for homing axis. F = Feed Rate/Probing Speed. T = Travel Speed.
M557 R116 S20

; Drives
M569 P0 S1 ; Drive 0 goes forwards
M569 P1 S1 ; Drive 1 goes forwards
M569 P2 S1 ; Drive 2 goes forwards
M569 P3 S1 ; Drive 3 goes forwards
M92 X80 Y80 Z80 E80 ; Set steps per mm
M566 X1200 Y1200 Z1200 E1200 ; Set maximum instantaneous speed changes (mm/min)
M203 X18000 Y18000 Z18000 E1200 ; Set maximum speeds (mm/min)
M201 X1500 Y1500 Z1500 E1000 ; Set accelerations (mm/s^2)
;M906 X800 Y800 Z800 E800 I60 ; Set motor currents (mA) and motor idle factor in per cent, It probably isn't supported in RADDS.
M84 S30 ; Set idle timeout

; Heaters
M305 P0 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 0
M143 H0 S100 ; Set temperature limit for heater 0 to 100C
M305 P1 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 1
M143 H1 S300 ; Set temperature limit for heater 1 to 300C
M570 H1 P30 T10 S120 ; Give more time to heat up
M302 P1 ; Allows for Cold Extrusion

; Tools
M563 P0 D0 H1 ; Define tool 0
G10 P0 X0 Y0 Z0 ; Set tool 0 axis offsets
G10 P0 R0 S0 ; Set initial tool 0 active and standby temperatures to 0C
;M563 S1 ; Allows for tool nomenclature compatibility between Slic3r and RepRap (Tools 0&1 vs Tools 1&2)

; Network
M552 S0 ; Disable network

; Fans
;Old M106 P0 S1 I0 F500 H-1 ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
;This is old M106 P1 S1 I0 F500 H1 T45 ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
M106 P0 S255 T60 H1 ; Hotend cooling fan: Enable to auto kick on at 60c (make it 'thermostatic'). 
M106 P1 H-1    ; Filament cooling fan: Must do H-1, or it'll turn on with P0 for some reason.
M106 P1 S0     ; Filament cooling fan: Must do, or it will go full blast on start

; Custom settings are not configured
M501
T0

; bed.g file for RepRapFirmware, generated by Escher3D calculator
; 16 points, 7 factors, probing radius: 116, probe offset (0, 0)
G28
G30 P0 X0.00 Y116.00 Z-99999 H0
G30 P1 X58.00 Y100.46 Z-99999 H0
G30 P2 X100.46 Y58.00 Z-99999 H0
G30 P3 X116.00 Y0.00 Z-99999 H0
G30 P4 X100.46 Y-58.00 Z-99999 H0
G30 P5 X58.00 Y-100.46 Z-99999 H0
G30 P6 X0.00 Y-116.00 Z-99999 H0
G30 P7 X-58.00 Y-100.46 Z-99999 H0
G30 P8 X-100.46 Y-58.00 Z-99999 H0
G30 P9 X-116.00 Y-0.00 Z-99999 H0
G30 P10 X-100.46 Y58.00 Z-99999 H0
G30 P11 X-58.00 Y100.46 Z-99999 H0
G30 P12 X0.00 Y58.00 Z-99999 H0
G30 P13 X50.23 Y-29.00 Z-99999 H0
G30 P14 X-50.23 Y-29.00 Z-99999 H0
G30 P15 X0 Y0 Z-99999 S8

I'm very impressed with this little piece of tech, if I can get it going, it'll save me so much trouble. Unfortunately, I can't test the probe with G30, despite it seeming to work on the effector end. The Green LED does react to tapping, and M119 says the Z-Probe is at min stop when not being tapped. Inverting M558 does not seem to get G30 to work, although it does lower the nozzle, I can't get it to react, despite the light turning green.

My electronics are the RADDS 1.5 + Arduino Due, with the dc42 fork of Reprap Firmware 1.21RC3.

I have literally everything else working. Fans, lights, hotend, thermistor, the works. I just can't get the Z-probe to work correctly!