The main characteristics of these configurations are:

The defined motherboard is BOARD_GT2560_REV_A_PLUS.
Travel limits are adjusted to the printer bed size and position.
An example SKEW_CORRECTION for a particular printer is enabled. See comments below about how to adjust it to a particular printer.
Using the LCD controller for bed leveling is enabled.
- PROBE_MANUALLY is enabled, which provides a means to do "Auto" Bed Leveling without a probe.
- The LCD_BED_TRAMMING option for manual bed adjustment is enabled.
- Bilinear bed leveling is enabled, the boundaries for probing are adjusted to the glass size, and extrapolation is enabled.
PRINTCOUNTER is enabled, in order to track statistical data.
INDIVIDUAL_AXIS_HOMING_MENU is enabled, which adds individual axis homing items (Home X, Home Y, and Home Z) to the LCD menu.
The speaker is enabled for the UI feedback.
bltouch variant:
- USE_ZMAX_PLUG is enabled. See comments about connections below.
- Heaters and fans are turned off when probing.
- Multiple probing is set to 3.

First-time configuration

Skew factor

The skew factor must be adjusted for each printer:

First, uncomment #define XY_SKEW_FACTOR 0.0, compile and upload the firmware.
Then, print YACS (Yet Another Calibration Square). Hint, scale it considering a margin for brim (if used). The larger, the better to make error measurements.
Measure the printed part according to the comments in the example configuration file, and set XY_DIAG_AC, XY_DIAG_BD and Y_SIDE_AD.
Last, comment #define XY_SKEW_FACTOR 0.0 again, compile and upload.

Print a suitable mount to attach the sensor to the printer. The example configuration file is adjusted to http://www.geeetech.com/wiki/images/6/61/3DTouch_auto_leveling_sensor-1.zip
Unlike suggested in geeetech.com/wiki/index.php/3DTouch_Auto_Leveling_Sensor, the existing end stop switch is expected to be kept connected to Z_MIN. So, the sensor is to be connected to Z_MAX, according to Marlin's default settings. Furthermore, GT2560-A+ provides a connector for the servo next to thermistor connectors (see GT2560 and GT2560-A+).
Be careful to respect the polarity of the sensor when connecting it to the GT2560-A+. Unlike end stops, reversing the connection will prevent the sensor from working properly.
Test and calibrate the sensor.
If using the GT2560-A+ and with the sensor connected to Z_MAX and an endstop connected to Z_MIN use the following calibration routine instead.

Home the printer with G28 command.
Disable the Z axis software endstop with M211 S0 Z0
Reset the probe Z_OFFSET with M851 Z0
Move to the center of the bed with G1 X100 Y100
Move Z incrementally until the nozzle is the correct height from the bed using a shim or piece of paper, record this Z movement, for example -0.2.
Do a single probe at the current point in the middle of the bed using G30 and not the returned value, for example 1.9. Invert this value, i.e. -1.9, and add it to the Z offset above, i.e. -0.2 in this example giving -2.1.
Update the probe Z_OFFSET to this value using M851 i.e. M851 Z-2.1.
Re-enable software end-stops with M211 S1 Z0
Save this value to the EEPROM with M500.
Update the start G-Code in your slicer software to insert a G29 after the last G28.
Carefully test that the offset is correct in the first print.