Hi Lanercost, there is a headstone for them in the old churchyard but unfortunately, it's only a marker stone with their names and the year it was erected. The inscription reads - "1813 erected by Robert Black and Margaret Dalziel his spouse".
The plot book records for the churchyard only begin at 1875 (but padded-out by some entries in the Day Book of the municipal cemetery from 1860+).
Each plot in the churchyard was divided into 3 sections (or lairs) namely the Centre, the North and the South.
So here are the entries from the Plot Book, the owners, in Victorian times, are recorded as Robert Black and Margaret Dalziel. All dates below are of interment, not death.
In the South -
MUNGO BLACK, aged 75 years. 19th March 1928.
In the Centre -
PETER BLACK, aged 70 years. 9th December 1879.
ELIZABETH BLACK, aged 65 years. 12th September 1883.
UNKNOWN CHRISTIE, no age given (most probably an infant or still birth) 12th march 1884.
MAGGIE BLACK, aged 16 months. 14th February 1882.
WILLIAM BLACK, aged 7 months. 21st October 1895.
In the North -
MARION BLACK, aged 62 years. 17th June 1902.
MARGARET BLACK, aged 76 years. 23rd September 1920.
I found some of Robert and Margaret's children in the cemetery Day Books, the information in these books is better.
SUSAN BLACK, pauper, Wishaw, aged 37 years, unmarried.
Parents - Robert Black & Margaret Dalziel.
Interred in the old churchyard on 17th June 1862.
PETER BLACK, carter, Wishaw, aged 70 years, married.
Parents - Robert Black & Margaret Dalziel.
Interred in the old churchyard on 9th December 1879.
(Peter may have been married to Elizabeth Wylie?)
MARY RUSSELL, Cleland, aged 75 years, widow.
Parents - Robert Black & Margaret Dalziel.
Interred in C322 municipal cemetery on 24th November 1906.
Also in C322 are -
WILLIAM RUSSELL, boilermaker, Cleland, aged 71 years, married.
Parents - Gavin Russell & Jane Brownlie.
Interred 11th November 1895.
LOCKHART BROWNLIE, modeller, Cleland, aged 32 years, married.
Parents - William Brownlie & Isabella Lockhart.
Interred 28th October 1899.
The stone with Robert & Margaret's name is in a very prominent position just underneath the bell tower of the now ruined church, luckily, it is just on the right side of the modern metal fence that was erected to keep the public from going into the unsafe ruins. The bell tower is a classic example of a 17th century Scottish "Birdcage" tower.