By sheer coincidence, Edison, you've come to the right place. I happen to have the drawings of the Southern Suburbs Redfern Station in my possession. First, it's very complex to understand, even with the drawings, so I'll do my best.
The SS tracks would have emerged South of Redfern, generally following the alignment of Wyndham St. Bradfield's ideas beyond that are included in his report to government, an original copy of which is available for reference at Sydney Uni's Fisher Library.
The best way to describe the underground stuff is to imagine you're walking the tracks. Let's look at the "up" SS first -
Travelling North on Wyndham, the track enters tunnel at about Chapel Lane, swinging to the right. Still falling, it enters Redfern platform which is on the right, still falling and veering right. After the platform it divides, deep below Lawson St. The left branch rises and exits the tunnel at the dive you refer to, between Lawson and Cleveland. The right branch proceeds u/ground to Central upper level.
The down track is just as complicated. Leaving Central, it emerges from tunnel South of Cleveland, merges with a surface track, then disappears ito tunnel at Lawson St. You can see the entrance to that tunnel from the Lawson St overbridge. Falling, it then enters Redfern platform, which is on the left, and which is at a much higher level than the formerly mentioned up platform. You can imagine passenger access to the down platform by going down the stairs to plats 11/12, where half way down there is a long vestibule. The wall on the west side is where the access to the down platform would be. After the platform, the track continues to fall till it meets the up track. They both then rise to exit at Wyndham St.
All clear? (hahaha)