..... and here's some more photos on the subject (to add to the confusion?) taken at the Spencer Street end. Shot 014 shows a brand new viaduct in use and that building on the corner of Flinders and Spencer Streets being built, shot 027 shows the siding into the fish market with the building at left named 'Department of Agriculture', and shot 038 (taken in 1929) shows a girder being transported somewhere, the fish market siding and the points leading to the now dismantled Flinders Street tramway.

..... and there's a photo of that entrance in the TDU archive attached to:
https://tdu.to/m/226633

Mal Rowe - noting that the photo also shows a more On Topic tramway linking the two stations.