Hi Mendy!
You can see the configuration files of GRBL I modified in order to make it work for Thor: https://github.com/angellm/grbl
However, these are the most relevant ones:
Steppers ENABLE/DISABLE signal
#define STEPPERS_DISABLE_BIT 1 // MEGA2560 Digital Pin 40
Steppers STEP signals
#define A_STEP_BIT 6 // MEGA2560 Digital Pin 28
#define B_STEP_BIT 4 // MEGA2560 Digital Pin 26
#define C_STEP_BIT 2 // MEGA2560 Digital Pin 24
#define D_STEP_BIT 0 // MEGA2560 Digital Pin 22
#define E_STEP_BIT 1 // MEGA2560 Digital Pin 23
#define F_STEP_BIT 3 // MEGA2560 Digital Pin 25
#define G_STEP_BIT 5 // MEGA2560 Digital Pin 27
Steppers DIR signals
#define A_DIRECTION_BIT 1 // MEGA2560 Digital Pin 36
#define B_DIRECTION_BIT 3 // MEGA2560 Digital Pin 34
#define C_DIRECTION_BIT 5 // MEGA2560 Digital Pin 32
#define D_DIRECTION_BIT 7 // MEGA2560 Digital Pin 30
#define E_DIRECTION_BIT 6 // MEGA2560 Digital Pin 31
#define F_DIRECTION_BIT 4 // MEGA2560 Digital Pin 33
#define G_DIRECTION_BIT 2 // MEGA2560 Digital Pin 35
Endstop signals
#define A_LIMIT_BIT 7 // MEGA2560 Digital Pin 42
#define B_LIMIT_BIT 5 // MEGA2560 Digital Pin 44
#define C_LIMIT_BIT 5 // MEGA2560 Digital Pin 44 //3 // MEGA2560 Digital Pin 46
#define D_LIMIT_BIT 1 // MEGA2560 Digital Pin 48
#define E_LIMIT_BIT 0 // MEGA2560 Digital Pin 49
#define F_LIMIT_BIT 2 // MEGA2560 Digital Pin 47
#define G_LIMIT_BIT 2 // MEGA2560 Digital Pin 47//4 // MEGA2560 Digital Pin 45
Tool signal:
#define SPINDLE_ENABLE_BIT 4 // MEGA2560 Digital Pin 7