I have no record of the FJ Powrie that you mention. I have an idea that he went from UK to Rhodesia and was not part of the South African Powrie group. The only male FJ Powrie that I have is born 16 April 1898 in Australia, so that cannot be the man in question. I am guessing that you have checked all of the records that I am able to check, so I cannot do better than you have already done.
Thanks for your affirmation of the great work that my mother did, but I must say that you have done a grand work yourself - far more than I have done. I am busy getting my mothers records uploaded (slowly) onto FamilySearch. A long process of checking what is not yet there. But, I am picking up some additional information as I go, stuff that my mother could not have checked because she did not have the wonderful resources available to us in 2009!
Alan Grose my (husband of cousin Gillian, daughter of Kathleen Enid Selwyn Powrie) is working on Dryden and Dymond, and he is doing a magnificent work there too. You both leave me to shame!