Well, I didn't get many -- make that any -- replies to my query, but that largely confirmed for me that no such image or more detailed written description exists, and I did not let it stop me from moving forward.
I know this is not the place for model or wargame related posts but since my original post was read more than 400 times I felt it would be right to follow it up with the final result, now that one exists. I hope no one is offended by me posting this here and if anyone is please accept my respectfully humble apology in advance.
Here's one photo of my 28mm scale version of the Sang-i-Nawishta
-- "Carved in Stone" -- monument, which stood at the entrance to the road through the gorge to which it gave its name: