Mark, Good to make connections...it's such a small world!
This is fantastic! You've done a lot of work on David Johnston...very helpful. I have some information on Jean Johnston McBrair, quite a lot on her daughter Eliza Edmondston, my gg grandmother... and on down the line.
The only resource on Dr. Johnston I can add is a history of the North Leith Parish Church published in 1993. It's called "North Leith Parish Church, The first 500 years" by Dr. James S. Marshall. Chapter 4, 'The Reign of Dr Johnston', is of great interest and includes a photo of a marble bust of him.I learned of the book when I contacted the church by email trying to track down Dr. Johnston's portrait. They were kind enough to send me a copy free of charge. If you're interested, I suggest you contact Norman Lindsay through email at the parish website.
Yes, I have heard from Richard Penney, please contact me at firstname.lastname@example.org.