It's a story detail, yes. Why would anyone who wants to feed you a story dress it up with so many nice round numbers? Are we to believe that the platforms were not potentially only approximately 10 feet apart? Probably not. The numbers as given matter enough to keep repeating them. It is why we have things which no one can even show that do have surviving descriptions and that still offer the opportunity to "puzzle" about them. The goal was likely that enough would survive to forever draw interest. What can we infer of a circular hole on a surface that is characterized with 9 levels of depth. Why place a symbolic polished rectangular stone of dimension 5x8 at that level? There are unrelated stories that might suggest you do that. Shouldn't that make us suspicious of a borrowing of detail?
There were not three boys sailing to an uninhabited island, but three is likely an essential starting story detail. No discovery of a hole was made in 1795, but the date, 33 years after the geometric planning and laying out of the Island in 1762 is probably an essential numerical detail to scream out MYSTERY (33 is the Western esoteric symbol associated with the "mystery of all mysteries"). 40 years from the arrival of the God fearing Rhode Island settlers for the discovery of the stone is probably an important numerical detail too. 40 symbols on that stone and rumors of treasure 40 feet below....An alleged marked off cross of 5x8 proportion with an internal 40 degree angle, surely repeats the 40 for some effect.
What do we actually know about the money pit story that is not numeric or geometrically given? It was located at the highest point of the island, 30-33 feet or so above sea level, depending on who you reference. You wouldn't have to specify anything else to know where to roughly find it. You'd certainly not need a million markers and criss crossing lines left on the ground to remind you. Why would it be necessary to be pointed to by an equilateral triangle of dimension 10,10,10 with an internal offset which cuts the base at 40% of it's length? Why have that pointer point N? Is it to tell us that the Cross asterism In Cygnus (at celestial declination 40 N) in the daily sets exactly below the horizon at N once a day at this latitude? Why repeat this detail that is found at still another monument located at the same latitude that OI is located at. Well, that's all very interesting to me. Having to mark out something at latitude 44.51N in Mahone Bay would require you to use that island if you wanted to be reasonably precise with a geo-metric suggestion. With some degree of consistency one can repeat what is found elsewhere there if you actually did want to draw attention to the symbolic cross of crucifixion in the sky as a beacon.
The legends leave us with details like circles and recognizable numbers we can familiarly attribute to regular geometry. 90 degrees for a straight angle. 30 and 60 as internal subdivisions of it which work as a pair of complimentary angles in a triangle. Near success at 111 feet., A "vault" located 153 feet that sinks into the abyss when approached... None of this is random in its symbolic association, and it most certainly not well measured enough to bother emphasizing it as a real empiric detail associated with real events. It would appear that symbols mattered more to the story peddlers like Reginal Harris than actual details over the years.
Step 1 at OI is using the historical record to determine the story does not compute. Step 2 is trying to understand why some details have survived to try and still be made to work on us. A lot of people are happy to stop at step 1 as it implies there isn't a treasure there (call off the searches). I'm surprised there are not more of those who would entertain step 2. Step 2 probbly has more to do with the intention of grabbing your attention after the fool's errands are exhausted.
I'm not sure what to say about those who successfully suspend their disbelief in the face a mountain of demonstrable refutations of the dubious details. It probably just means that those who want to believe will never be dissuaded from going on a fool's errand.