Hi Arranroots and everyone else. Having just joined after reading your thread, I too am interested in the Hastings of KKD and may have a link of interest.
My great great grandfather, Archibald Hastings is the son of John Hastings and Elizabeth (nee McMillan).
I have a copy of his marriage certificate (1863) at the age of 23. At this time his father, a grain miller, is listed as deceased.
Both Archibald and his new wife Mary (nee Selkirk) are listed with a usual residence of Maxwelltown.
I am assuming therefore that Archibald is the brother of John (your relative) and that we have a common ancestor in John Hastings Snr and his Father (according to your post) Archibald born in 1739.
If this is indeed the case I would be grateful for any information you may possess on this line of the Hastings.
Of course if you need any of my somewhat limited information I would be more than willing to help.