The rail for Maroona to Portland is 47kg and was laid in the 1970's or 1980"s? As compared to the very old (1919) 41 kg on Maryborough to Ararat.
That said, I would give the project to the ARTC and go for 60kg rail on mainline concrete sleepers. This then would allow a speed of 100kph on a 23 ton axle load. You then have instantly (and completely) integrated Portland into the national rail freight network. So the Port of Melbourne get some overdue competition.
Another advantage is that any ideas of turning Western port bay into a rail freight hub are over. So a fragile Eco system is protected.