This is the entry in the Churchyard register, looks as if they had a "slab headstone", not sure if this means laid flat and might now be covered over. If you don't have a Findmypast account then you can view entries on the site in many Libraries, Archives for free including all LDS Centres. https://search.findmypast.co.uk/record/browse?id=gbprs%2fply%2f004635151%2f00157