Hi Peter,
Did you make any progress researching your ancestor? I think he might be the son of who Amelia calls "Gregour Roy in Callichra" in her History. I think the witness Dugal is Gregor/John's grandfather, and Malcom his brother. He was not related to Rob Roy through the paternal line, but his brother appears to have been outlawed with Rob Roy, as there is a gap between 1714 and 1723 in his family. Maybe Gregor/John was also with Rob Roy, especially as his two sons appear to have been with Rob's son James Mór;
1728 Dugall/Agnes Buchanan Mary Innervonichell Killin
1729 Dugall/ Ann Buchanan Gregory Corrycheiroch [Coirechaorach] Killin
1729 John/Christian Duncan Innervonichell Killin
James signed as James Drummond Tacksman of Coriechormich in 1729, (the ruins of which are called Rob Roy's House locally), and had a family with Annabell McNicoll at Innervonichell from 1731.
I think Gregor/John' sister Kathrine was the second wife of James Grame alias Gregor McGregor in Ashlan. He also has a gap with his first wife between 1715 and 1720, and his sons also appear to have also lived in Strath Fillan, and then the Braes of Balquhidder, and I think they later changed their name to Drummond, and then Grierson/Gregorson.
Does this match your records?
If you want I can post how I arrived at this conclusion, using the baptism witnesses of the families above and Amelia's History.
We actually spoke about Rowchnock several years ago, but takes me a while to process information.
John.