George Muir is buried in the little "Private" walled burial ground that sits between the old churchyard and the new cemetery at Cambusnethan. I don't think there is a gravestone but I will go and have a look. I have photographed many of the stones there but have nothing on file for him.
The following information is taken from the gravedigger's day book -
GEORGE MUIR, waggon greaser, Wishaw, aged 66 years, married.
Parents - William Muir & Margaret Donaldson.
interred in the Private, plot 310, on 8th August 1866.
Also in that plot are the following -
WILLIAM COLE, miner, Watsonville, (parish of) Hamilton, aged 56 years, married.
Parents - John Cole & Agnes Ruedick.
Interred in Private 310 on 23rd May 1874.
MARY MUIR, housewife, Glasgow, aged 79 years, widow.
Parents - James Brown & Rachel Paterson.
Interred in Private 310 on 8th May 1883.
Hope this helps? I have no idea who William Cole could be. Watsonville, although technically in the parish of Hamilton at that time, was actually in the town of Motherwell.