Despite the fact that there is obviously a school in view here I was having a really hard time trying to read the name, however, as it turns out I was able to match the angle of the road with Lion Rock in the distance and came up with some possibilities and so ended up matching it that way instead (talk about making life difficult for myself). Anyway, it turns out the school is the St Rose of Lima's school on Embankment Road.
The muddy verge on the left looked a bit like the railway track to me and low-and-behold, it was the embankment that holds the KCR track through this part of town. Of course, the track has undergone many changes since 1965 but even from Streetview you can get the same kind of feeling for the place.
The apartments that the guys run into are still around and they are called Duke Garden - built circa 1964, so they were pretty much brand spanking new when Cosby and Culp ran through the gate.
The current Streetview gives a good view of the area - and it hasn't changed that much really, but unfortunately the school appears to have been under scaffolding when the Google car was doing its rounds.
Okay, so the embankment is now covered in walkways because the railtrack - once a common thoroughfare for people walking places - is now off limits courtesy of modern high speed trains and high voltage powerlines. But thanks to Kowloon Tong's historical low-rise development, we can still see Lion Rock in the distance (although these days the smog does an equally good job at obscuring it). Duke Garden still stands in place but the school itself - under scaffold in Streetview - has since been completely rebuilt and no longer looks the same. If you are a bit unsure as to where this place is, then directly the other side of the railtrack is the Yuen Po Bird Garden (shockingly awful place if you ask me full of illegally smuggled birds) and the Flower Market.