According to SP William Clark was born on 14 September 1858 the illegitimate son of Margaret Clark the daughter of John Clark in Dunkeld.
In 1861 William is with his grandparents John and Christian Clark in Dunkeld.
In 1871 William is with his widowed grandmother Christina in Dunkeld.
In 1881 William is a joiner living as a stepson of William and Margaret Forbes in Dunkeld.
I can't find the ship he went to NZ on but I hope this helps.