Up till now I hadn't searched TROVE but it has proven to be a great source of information connecting Robert to the area of Echuca.
It looks as if he managed to take some of his children with him. Peter is mentioned in the probate details. So Isabelle, Peters younger sister, may well have travelled too. Perhaps even more of the older children which could all lead to a Clark family in Victoria?
I'll continue the search.
many thanks.