I'll take a look at converting it later tonight and take screenshots of any tips and tricks of interest, and the file itself if it works nicely.
I've been wanting to make a 'Cardinal's Curio' of little misc tutorial snippets that don't necessarily need to belong to any one set of instructions, so I don't mind writing up stuff I can reuse in that

Please let me know if you have any luck with it. My attempt still leaves me extremely frustrated, although I will probably use it anyway.

A little later than anticipated, reset my PC and it took a while to get everything sims related resituated, but here are my findings:

As you can see, even if I considered this a relatively straightforward conversion and it didn't take me all that long (about an hour or two, which is including those Blender troubles, using TSRW when I usually don't, testing ingame, discovering the CFIR trick on my own, and redoing from scratch while I wrote out these steps) it's sort of gargantuan to have in writing. Which is probably why tutorials that specific are few and far between. It can look like a bit of a major, but once you are familiar with each of those tools it kind of flies by.
Most of the same steps would apply for a decor piece, but after using an EA fireplace as reference for placement you would import into a clone of a decor object instead- usually a sculpture.

I've attached my conversion, but it still has it's share of little issues. I don't really recommend anyone but OP use it for learning purposes.
The dropshadow comes out too far, and I don't know how to do footprints/bounding boxes in TSRW so the external chimney generates floor/foundation in the wrong spot and things can clip into the sides. But you are free to take it apart, modify it, do whatever you like with it.
With moveobjects you can delete the chimney parts, and in that case it's not too bad looking- here's a screenshot of it looking absurd in Constance Shelley's living room.

Thank you so much! I am going to try to follow your instructions and see if some knowledge can't seep into my head.

Okay, I've been away from the computer for family and holidays and blah blah blah.

I've got blender 2.7 installed. When I go to the Blender page, it wants me to install 4. I can't find "geometry" on 2.7. I'm hesitant to install 4.

Here's a screenshot of what the option I referenced looks like, on the pop-up for importing a Wavefront Object (.obj) :


But for future reference, the great thing about Blender is that every version is standalone rather than a cumulative patch as we'd usually understand it. You can have as many installations as you need for compatibility with whatever it is you are working on.
Long term support versions can be found here: https://www.blender.org/download/lts/
Versions older than LTS are here: https://www.blender.org/download/previous-versions/