Where: Here's the same view today, looking east from Stubbs Road across Happy Valley:
You have to look carefully to find any matches between the views. The two I found are both on the far side of the valley:
- In the centre of the new photo you can just see the spire of St. Margaret's Church peeping over the top of the racecourse stadium
- And to the right of that you can see the slope of Broadwood Road as it climbs the hill.
What: In the top-left corner of the old photo there are two buildings on top of Leighton Hill, the Leighton Hill Government Quarters. With clear views east, west and north, they must have been a fantastic place to live.
There had been earlier government quarters built on that site, but they were destroyed during the fighting in 1941. The Leighton Hill ridge formed a natural defensive line against the Japanese who'd landed to the east at North Point and Quarry Bay. The ridge was staunchly defended against repeated attacks, and by the end of the fighting was described as "looking like the Somme" .
Remarkably, there is a wartime relic visible on Leighton Hill if you look carefully. Can you spot it? And what was it for? Ifu'll post the answer after the weekend in the comments below - unless someone beats me to it.
Moving further right along the ridge we come to another pair of tower blocks that I don't know the name of. These are newer, with the construction scaffolding still in place. Can anyone identify them?
Right again and slightly down, and we get a clear view of St. Margaret's Church. Then opposite the church are the dark roofs of more government quarters. These ran along Ventris Road and survived into the 1980s. Here's a close-up from 1981, taken by Andrew Tse:
Above them is the sloping Broadwood Road that we mentioned before, with several grand houses along the ridge above it. I believe these were part of 'The Ridge' development, which was connected to C.E. Warren. 
Looking down from the buildings, the central third of the photo is taken up by the Happy Valley racecourse and its stadium. The grassy area in the centre of the racecourse is marked out with pitches, and we can see several pairs of goals. Would they have played football or hockey (or both) there in the 1950s?
Who: There are several people visible on the pitches. Not enough for a match though, so are they practising? Or were the pitches open to the public for recreational use?
Just in front of the stadium's clock tower are a much less active group. Zoom in to the clearing, where you'll see several rows of graves in the Hong Kong Cemetery.
When: We know the Leighton Hill Government Quarters were completed in 1948. And the Jockey Club's website says that this stadium was "replaced in 1957 with two seven-storey structures" . So we're looking at some time between those two dates. If we can find out the construction date of those two blocks in scaffolding, that will help narrow it down.
What else is there to see in this photo?
- Tony Banham's "Not the slightest chance", page 286.
- Charles Edward Warren
- HK Jockey Club History (look at the entry for 1931 on the timeline)