When I searched for the church deed, I could not find any sales by John Oxley in 1871. However, I did find a deed from John Oxley to John Black, Thomas Donkin, and 4 others for a 1/2 lot for a church and burial ground in 1817. This deed is identical in wording to the deed transcribed in All Mines and Great Pines except the 1817 deed also mentions that the 1/2 acre was on Lot eleven. So, it's possible that the deed that hangs in the church was for the original church site on Lot eleven and not for the current site.
I have updated the Lots 16 and 17, River Philip page on this website with this information.