Hello Icon,
You are out of luck I'm afraid, there is, as you say, nothing in the MI book (which was compiled in 1982 - 83) and the parish mortcloths list only begins about 1742.
There may well have been a headstone for this family but very few have survived from that time in Cambusnethan. It may well have been a flat stone which has disappeared into the ground over the centuries, covered by a couple of hundred years of grass and leaves.
There has been much vandalism in this churchyard and many of the sandstone monuments have simply eroded away. Take a look at this photograph, it is number 40/1 in your MI booklet. The inscription was perfectly readable in 1982.
There is also the possibility that your ancestors are buried at the ancient burial ground at Kirkhill. This was the place where the original pre-reformation parish church was sited. It was abandoned mid-17th century but the burial ground continued to be used right up until mid-20th century. The stones there have been subjected to a century of vandalism of the most extreme kind. The biggest culprit being the former burgh of Motherwell & Wishaw back in the 1960s, who allowed a great many of the stones to be bulldozed into a corner in order to accommodate a sectarian march.
There are some Gourleys buried in this ground but none as early as the date you give.
