mikejurasw-
When you are dealing with older homes, there are some very strange wall and ceiling/roof construction methods. It is not a regimented and close-minded as current construction. The older homes often had details that were dictated by the general plans local practices and materials.
I had an older 1400 sf home (built in about 1915) that had many unique details and construction methods. It was similar to your home in terms of strength, massiveness and thermal inertia. It was cheap to heat and cool and very comfortable. It was so low, that I do not even remember what the cost was.
At first, every time I drove a nail or opened up something, it was an adventure. - My wall construction(outside to inside) was a very rough stucco applied to10" or 12" hollow clay tile (tile cores running horizontal), full dimension 2x4s, lath and plaster with a very smooth and hard surface. A woodwork (modern Greek style using beautiful maple as wide as 12") was painted and not stained or varnished. The structural flat roof (no parapet walls) was about 24" above the ceilings was gem with not signs of leaks and the 2 roof drains were 4" cast iron that ran down an interior wall into the sewer system.
I am sure you are finding some unique and costly items as you open up things.- I bought mine for $23,000 in about 1968 and sold it for about $50,000 in 1975. The last sale was over $500,000 and it still looks the same as it did in when it was built.
Dick