Wholly mole wow that's a mouthful of stuff! And I don't know what any of it means!
Anywho, as for the volumetric mass of the fireplace.... I drew it up in Open Office (similar to MS Office PowerPoint); Open Office let me add the "Wall" stone print on the facades of the shapes
These are the measurements that I find on the fireplace as it is INSIDE and OUTSIDE the house, including the depth of the stone from the outer edge in the room to the surface of the wall, as well as the depth from the outside wall to the outside edge of the stone.
We are looking at volumetric mass of 183,986 cubic inches, though we probably need to also account for the missing volume of the flue. In any case, that cannot be too significant. I've already accounted for the firebox carve-out, so I believe that whatever might account for the flue is de minimus. Also, though I did account for the firebox carve-out, I MIGHT have put back some of it in the measurement of the outside wall, since I cannot see for sure how much of that exterior mass the back of the firebox might be taking up. But in any case, it should still be insignificant.
I think I've got it right. Can anyone confirm if I calculated the volumetric mass correctly?
I could also load more stone into the firebox, around the chimney pipe and against the walls, maybe a little more on the floor too.