Ok, no idea why he used a servo pin for it, but has nothing to do with servo. As I said pins may have names but get function you assign, so any free pin works. Only important is that it is configured as input and you do not exceed 3.3V.
So you want to go with z probe only. Just unplug z min endstop and put your z probe signal pin to z min pin. Select pullup no and check if signal is ok using M114. If it is H when not triggered invert endstop.
Assign z probe also the z min pin, so firmware knows about the special condition. Also set pullup/signal same as end stop so M114 signals it right.
As a first test run G30 with a metal holding close to sensor to stop before you reach bed. That way you have time enough to reset printer if it does not stop. Do the same for z homing. When you know it works you can let it go down to bed for testing.
