Sticking your finger in the hole is much easier and less time consuming than trying to stick something in there to measure the distance. IMO
Stick your finger in the hole lightly touching the side of the gear. have a buddy slowly turn the crank with a breakerbar (take most of the sparkplugs out to make it easier to turn) . Eventually the side of the gear will raise up, or go down. (half of the gear is lower than the other half). Once you are sure the raised section is over the hole, stick the sensor in untill it contacts, then just back her out a hair before tightening.