Hi Keith
I have been researching my family as well. The name, Peter Gibson Grant Clark, was familiar to me.
You may be searching for this same person.
Here is the information that I have developed.
Peter Gibson Grant Clark
B:17 May 1929 Moffat, Dumfries-shire, Scotland (illegitimate)
D:10 Apr 2006 Bulawayo, Matabeleland North, Zimbabwe
Mother:
Marion Jardine Clark
B:12 Oct 1900 at Harthope Place, Moffat, Dumfriesshire, Scotland
D: unknown
Father (suspected):
William David Johnstone
B:15 Mar 1898 Durisdeer, Dumfries-shire, Scotland
D:12 Jul 1953 Port Colborne, Welland, Ontario, Canada
Maternal Grandparents:
John Clark
B:17 Jan 1871 Blacksteps, Dunscore, Dumfriesshire, Scotland
D:26 Mar 1929 at 2 Rae Street, Moffat, Dumfriesshire, Scotland
Margaret "Maggie" Gibson Grant
B:19 Oct 1873 Moreland, Moffat, Dumfriesshire, Scotland
D:18 Sep 1943 at 31 Ettrick Drive, Moffat, Dumfries-shire, Scotland
Paternal Great-Grandparents:
Robert Clark
B:Abt. 1844 Keir, Dumfriesshire, Scotland
D:6 May 1910 Blacksteps, Dunscore, Dumfriesshire, Scotland
Marion Jardine
B:Abt. 1842 Kirkpatrick, Irongray, Kirkcudbrightshire, Scotland
D:11 May 1894 Blacksteps, Dunscore, Dumfriesshire, Scotland
Maternal Great-grandparents:
William Ronald McDonald Grant (my 2GGF)
B:15 Jun 1831 Dumfries, Dumfries-shire, Scotland
D:26 Aug 1893 at Harthope Place, Moffat, Dumfriesshire, Scotland
Margaret Gibson (my 2GGM)
B:Abt. 1835 Howslack, Moffat, Dumfries-shire, Scotland
D:7 Nov 1912 at Causeway Street, Moffat, Dumfriesshire, Scotland (usual residence - Viewfield, Moffat, Dumfriesshire, Scotland)
According to the 1901 Scotland Census, John and Maggie (Margaret Gibson Grant) Clark, along with infant daughter, Marion Jardine Clark, lived with Maggie's older sister, Janet Gibson Grant (my GGM).
Also living with Janet Grant were her nephews, James Dewar Grant [B:14 Oct 1894 D:9 Mar 1922] (Maggie's 6-yr-old illegitimate son), Thomas Inglis Grant [B:31 Jan 1889 D:17 Jan 1909] and Janet's son, Thomas Gibson Grant [B:15 Oct 1881 D:23 Oct 1972] (my paternal GF).
I hope this is helpful to you.
Alan