Hi Sally,
Did you ever have any luck finding William Legender Milburn? You probably already have this but just in case you have not maybe the Papers Past, Star 20-2-1889 will help. The account of his drowning has him as being "in the colony for four years". So he must have come out 1884 - 85.
He is buried with his uncle, Morris (Maurice) Milburn, Woolston cemetery, Rutherford St, Chch. Morris came out as a single man aboard Zealandia" 1859.
Cheers Kay