AC-Studio has a great shot of Happy Valley taken around 1950 I guess. In the foregound is Tung Lin Kok Yuen, a Buddhist nunnery and school built in 1935, and the Jewish cemetery, together with its little chapel. The graveyard was first laid out in 1851 and expanded some 50 years later. All of those are still there. In the distance is Blue Pool Road. The houses lining the far side of the road have long gone; those who know the area will recognise it as the long-empty spot above the bordering granite wall where construction has recently started on a residential development.
Interestingly you can see areas just below the road that look like they're cleared for squatter housing or small vegetable plots, this can still be seen above one of the tunnel portals below the road today. You can also see a path wandering steeply up the hill to Broadwood Road. I'm guessing the year.