Hi Shannon
Welcome to Rootschat.
I have researched the Thomas Henry and Jane line fairly extensively as it is my line and have not come across a Stanley Keith anywhere.
There is a Stanley Lewis CLAPHAM in the Joshua line who was in Gisborne, son of Joshua and Emily, born 1898 and died 1973. He was married to Audrey Edith SKELTON, who is also buried in Gisborne.
The NZBDM has a death for a Keith Stanley CLAPHAM in 2001, with birthdate given of 24 May 1929. Is this your grandfather? The marriage records have him as Keith Stanley as well.
Stanley Lewis CLAPHAM and Audrey Edith SKELTON were married in 1928, so it is possible that they are the parents of Keith Stanley/Stanley Keith.
Ian C