At Murrarie which is roughly half way between Moorooka DG passing loop and PoB there is roughly a 800m long NG loop.
It is still connected to the DG from just prior Murrarie station to just past the closed but still in place branch to the Incitec.
(last I saw a few years back the signally was still working or at least lite up including the branch line)
The NG track then continues to follow the DG as a siding for another 700m or so finishing at a buffer stop.
So this passing loop could be used to allow NG coalies and SG to pass each other or it wouldn't take much to both reactive the NG passing loop for SG and the coalies to pass each other
Completely rebuild the loop and siding to DG 1.5km long passing loop and potentially extend to 2.0km if required.