Why is K Road in Werribee South called K Road?
Unfortunately, no contemporary documentation can be located in relation to the naming of early roads in this part of Wyndham.

A 1908 map held by the Public Records Office Victoria (PROV) indicates a grid system in use for the division of the Werribee Park Estate at that time.
https://prov.vic.gov.au/search_journey/select?keywords=c437r

In the 1890s, the Chirnsides began to divide up excess land in the Werribee Park Estate and created large allotments which were sold or leased to farmers. Grids with alphabetic references to A through G are clear on the map. The gridlines run roughly east-west across the estate. The relevant map is marked C347R.

As noted in the local press, by September 1931, a section J also existed in the Werribee Park Estate.
Werribee Shire Banner, 10 September 1931, p.4.

It is possible, but not certain, that by 1931 a 'section K' also existed in the Werribee Park Estate, and that the east-west section of K Road, running from the Werribee River to what is now Point Cook Road, retains both the direction and east-west extent of the original K Road.

At some time after 1931, once the land divisions other than K were no longer current, K Road appears to have been extended north to meet Duncans Road, thereby completing the extent of the modern K Road.

Regrettably, neither Wyndham City nor any other organisation has published any definitive evidence around the naming or original character of K Road.

The above information is compiled from several sources and, although it is backed by some contemporary evidence, cannot be completely relied upon.