The work of William S. Buehler has been mentioned previously, and Bill has been highlighting a grid possibility incorporating the River Almond and Cramond at its mouth. He has also in the past described a system using the Lindisfarne (NT 136 422) - Duart Castle (NM 748 353), on the island of Mull, extending from there to both Iona and Staffa.
Whilst in Google Maps I decided to plot this line and see where it crossed the entral area of my focus, and what else was included.
Using several points I calculated their relationships with both Lindisfarne and Duart Castle. Omitting detailed calculations for now, I found that the line from Lindisfarne to Duart Castle passed between Arthurs Seat and Inchcolm, and precisely the northern tip of Cramond Island (NT 197 787), some 68 yards offshore, at a distance from Lindisfarne of 63.5 miles(E).
(As I did this exercise I saw the line as a guitar string being plucked and vibrating between Arthurs Seat and Inchcolm, like a gate mechanism, limiting the pitch of the string.)
Other points of interest on this line Yester Castle, Musselburgh, Devilla Forest/Tulliallan Castle, Port Of Menteith, Ben Vorlich.
The line is on the Google Map on the Preston Cross triangle page. I need to limit the number of G-Maps I include as they slow loading down too much!
This is just a brief note on this topic, for now!