As it turns out, finding it was not difficult! It still exists today and is known as Half Mile Bridge. And it's not the original bridge in this location, but was built in 1928 to handle the heavier engines! (At least, as per this story - perhaps more interesting if you are into trains. Are you a ferroequinologist?
I could have got a 'closer to the original' photo if I had walked up the valley (or had hovered over the on-ramp to the Don Valley Parkway), but the picture below is from just below Chester Hill Lookout and is recognizably the same bridge. Maybe I can stop on the DVP one day and take a picture from the ground (at the bottom left of the picture below). I'm sure traffic won't mind ducking around me as I stop on the on-ramp there.
Some other pictures and stories (e.g. of walking over it) can also be found here. And for those who long for a litlle colour in these stories of yesteryear:
