From Muriel Leo’s (nee Oliver, 1917-1998) Family Tree.
Dax Eric Clayton Lloyd, (great-grandson of Jessie Bertha Oliver b.1876) lists John’s name as Jack although Rachel Frances Oliver born 31 August 1940 confirms it is John William.

Dax later writes name as, John William Sycamore:
“Here is his birth registration;
Registration Number: 1903/10805
Family Name: Sycamore
Given Name(s): John William
Mother's Given Name(s): Mary
Father's Given Name(s): John William”

“Which gives his parents names.
Here is their marriage registration, which gives both full names;
Registration Number: 1884/1825
Bride's Given Name(s): Mary
Bride's Family Name: Black
Groom's Given Name(s): John William
Groom's Family Name: Sycamore”

“Here is John's cremation record from Pyes Pa, Tauranga;
Record Type: Cremation
Full Name: John William SYCAMORE
Age: 82
Gender: Male
Date of death: 29/08/1985
Funeral Director: JONES & COMPANY FUNERAL SERVICES
Cemetery Name: PYES PA
Plot Location: Not Specified
Date of Cremation: 29/08/1985”

Full date and place of birth, date and country of marriage, from:
https://www.wikitree.com/wiki/Sycamore-31