Began measuring so I could transfer measurements to the other side. Used a square to go from the hole down to the bottom, center-line & made a mark. First measurement works out to be almost exactly 6" (15.24 cm) back from the tailwheel strut.
A word of caution. These measurements are for my Singleton Apparatus location and my tailwheel location. The odds of your pieces being in exactly the same locations, permitting exactly the same measurements is highly unlikely. Take care and do your own location work.