WRT the Tarcoola/Alice line, the Highways Dept was planning, designing and constructing the new Pt Augusta/Alice Hwy around the same time. My colleague was the Planning Engineer in charge and I recall him shaking his head in disbelief at the lack of culverts under the adjacent sections railway line cf the provision made for the road. This was particularly apparent across flood plains where there was a lack of distinct watercourses but local knowledge indicated the need for regular culverts. A sort of "if it isn't obvious, it doesn't exist!" approach. Even after he gently offered his observations, nothing was done. After the flooding, the road suffered no damage: the railway - another story
The Alice Springs - Darwin railway was built on a shoestring budget. They cleared the right of way, laid the track, and didn't do much else.
They used light rails (50kg), wide sleeper spacing and shallow ballast. Such sidings as necessary were put in, and no more. No allowance was made for future growth.
The usual practice in railway building is to clear and grub, install culverts in all depressions in the landscape, and then build the earthworks. On this railway they did the earthworks first, and then dug up the roadbed and earthworks to put in culverts. I'm not surprised they skimped on culverts, it fits with the ethos of the project.
The attitude regarding sidings was put them in as traffic demanded. I reckon the same applied to culverts -
put them in when and where they prove necessary.