Your not good at this are you, what would make you think that the 90' stone would be nothing more the a enticer? What happen when they dug past the stone? Water! Water that they can't stop. Man's greed, they relied on man's greed to open that flood tunnel. Look at the Shugsbough monument, a positive depiction of the Shepherds of Arcadia by Poussin. What are the shepherds pointing to? The "Stone Carving". The words "Et in arcadia ego", translated " "Even in Arcadia, there am I" which has been described as poor latin. There has been a theory that the words are a anagram, Tego arcana Dei, meaning "Begone, I keep God's secrets!" I had a computer translator do it and I got "I cover the secrets of God". It was a explorer by the name of Giovanni da Verrazzano who first called the eastern coast of North American "Arcadia", in 1524. commissioned by the king of France, King Francis I, to explore the new world and look for a new trade route to far East. Some believe that he was sent to look for signs of the Knights templars that went missing in 1306.
The Shugborough monument has the same dedicatory D M as other Latin monuments and tomb inscriptions. Typically, this means: "Aux Dieux Manes" which is an address to all of the deceased Gods of the Ancient world, or to the spirits of the deceased in general. It make sense to have Poussin's image on this tomb because "Et in Arcadia Ego" is in fact a memento morti painting/scene which is about remembering death. The scene is taken from Greek myth and suggests that all is not well in Arcadia (the lamb is lost). The counter suggestion is the one that says that the shepherd (the son of God) will come again and finds his lost lambs to reunite them all in heaven.
There's a parallel between that and the Aelia Laelia Crispis monument plaque located at Bologna (at the same latitude as OI, 44.51N, incidentally). It too addresses DM, all the Gods of the ancient world, who have now been replaced with something else (the Christian God). In that case it is a lamentation. It makes sense as a Renaissance esoteric work that is part of the counter current to the Church of Rome which rose in Italy at this time. A lot of the controversial esoteric works/paintings did that. Poussin's work is assuming to be doing that too. It's a Baroque era painting that has a well known geometric composition that is meant to suggest the thing that has come and replaced the pantheon of Gods of Antiquity, namely the Trinity. The geometric shape used to do this is the arbelos which famously comes out of 3 circles. What the shepherd points to in the image is the center which is also the center of the large all-encompassing circle (a monad) that contains the desired geometry. This echoes the idea that God's plan has a natural equivalent in the geometry we see evidence for in the world.
The painting's composition exploits the divisions produced by the geometric construct that defines the arbelos. You can see that here:
This is in no way rare for a painting of this date. Using symbolic geometric armatures was all the rage at this date. "ET In ARCADIA EGO" does have a anagram solution, but only one. "A GENERA DIATONIC". This would seem to want to send us in the direction of considering the key of A in music, as the genera is the key to which a harp/Lyre is tuned. The diatonic scale is the normal musical scale. In terms of similarities, you might want to suggest that there is an octave of characters on the Shugborough monument as well as a grouping of 8 "words" on the fictitious 90 foot stone with 40 characters. The extreme range of the human voice is about 5 octaves. 8x5 does equal 40, so that's at least quite reminiscent of the invention we have been given for the 90 foot stone if we wanted to suggest some sort of inspiration for it. Continuing on the musical theme, A is 440 Hz in our standardized music. In the scientific tuning it is 444 Hz. One could suggest that this is given as a "clue" to 44.4N as a latitude. This may please those who might see a eerie parallel with the fact that 66.6 W of Paris and 44.4N places you smack dab in the middle of Mahone, Bay, NS, on a very interesting Great Circle. 44.4N and 66.6 W are in ratio 3:2 which is the Pythagorean harmonic that underpins all of music. 44.4 +66.6=111, and that is quite harmonious if we consider that all terms are divisible by 11.1 to give us 4, 6 and 10. 4, 6 and 10 are the divisions of the base of the Welling pointer that points N on OI.
Anyway, there is nothing in any of what you mention that involves anything but referencing earlier existing works of esoteric interest. The Bologna monument, Poussin's composition, the Shugborough borrowing and the geometric suggestions at OI mesh quite nicely in terms of symbolism. That is really bad news for anyone who is fond of a treasure story buried by some ruffian(s).
I would argue that the fact that Morris' survey of 1762 aligns so well with the presentation of a similar geometric theme (arbelos based) does inform us about what is going there. Where there are lamentations in other places about the fact that the Christian God has replaced the old pantheon of Gods of Myths, but the exact opposite seems to be suggested at OI by Freemasons. In many ways it is about celebrating what the Welling pointer points to at N, which is a symbol of the Christian God who will rise/come again. That would be the Northern Cross, symbol of the crucifixion, which sets exactly at the Northern horizon each and every day at 44.51N. It is paid homage to on land by a cross that points along the heading of the great circle to Jerusalem. OI is about finding your bearings in many ways, it would seem. Its terrestrial bearings are being appreciated for their symbolic value to promote the Freemasonic views contained in the Holy Royal Arch degree which was contained in the colonial era Freemasonry (the 4th adjunct degree).
1762 is a perfectly fair guess for when the surveying was done if we had not been given it precisely by history. Charles Morris did it in his role of surveyor general. By all appearance it is retelling a story that Morris had been initiated to by Erasmus James Philipps who brought Freemasonry to NS in 1742. In many ways OI has lost it's meaning for the masses and it is only too appropriate that something that was once used to promote a burning Christian piety has been turned for us into a cautionary tale about digging for lucre and losing one's life for material wealth in the process. Thomas Haliburton likened the moral we should take from the OI story to Bunyan's 17th century work, "The Pilgrim's Progress" in 1847. Do not die buried in a shaft on a hill of lucre looking for what no man can even name, and do not go off the straight and narrow path into the mud of the swamp looking for what might be buried there, else you drown in the mud. How well did he understand what was going to come out of the Archibald's stories at OI?