Trevor, I have had a look thru the 1910, 1938, 1948 and 1973 SAR General Appendix to the Rule Book's that I have and none make any mention of "poling" or "pole shunting" or the use of "poles", the American "poles" I believe were something like 12' long x 4" diameter Oak with steel bands at the ends, I certainly have never seen any laying around the yards or Islington, and as you well know, Islington was a treasure trove of old stuff before the great ANR(C) clean out. Funny enough though Trevor, when I googled "pole" and "shunting" all manner of electrical gobble de gook came up about "poles" and "shunts" that would have related to your Electrical era, but no "pole shunting".
It would not have been a form of shunting that I would have liked to participate in, the thought of holding some heavy beam up and in place in one poling socket and aim it towards an approaching socket like some medieval knight in a jousting contest sounds a lot to scary for me,.
I believe the 720's were the only engines so fitted (500 class diesels certainly weren't), for it to be used for shunting a similar "socket" would have to be fitted to wagons being shunted and that certainly wasn't the case.
I thought that the bible's may have mentioned which stations had horses to see if Pt Elliot was allocated one but I couldn't find any reference.
Catch you soon.