Well...
There are maps and there are maps. They appear to be only as good as the cartographer.
I found a 2015 map that has Gower Street going all the way from Berners Street to William Street. It may have been copied from a much earlier map. And an older Google map has Clifford Walk on it.
I went to Gower Boys in the early 70s and Clifford Walk was there.
Below is a snip of the 1888 map that Lyn kindly directed me to showing all three school buildings.
The workshop building is to the right of the Church on Lozells Road confirming Banjo's graphic.
View attachment 155266
As I mentioned to Janice, the street names are more often than not, equidistant from each end of the road on maps.
So I concede that the Annex building was on the corner of Guildford and Gower streets as shown above.
Now I am interested in finding out when the last section of Gower Street changed it's name to Clifford Walk.
I suspect the change happened well before the 70s Janice because there was nothing new about Clifford Walk when I went to school there.
View attachment 155267
It appears that Gower Street is being eaten from both ends. I am not so interested in Old Postway as that doesn't have anything to do with the school.