I am not ready to replace the stairs yet, but I wanted to finish installing the casings on the living room door, and be able to finish the drywall on the bottom few inches of the dividing wall, so I decided to remove the bottom 2 steps.
Since these stairs were not properly installed, the bottom 2 stairs were a mess.
Here's where things get interesting. OBVIOUSLY, the stairs never went past the living room door (as they did now), and here you can see that there is original hardwood with ugly brown carpet covering it (the rectangle cut out of it was something I did the first year of owning to house, but it was one full piece). Obviously someone didn't carpet UNDER the stairs, so this was remuddled later.
Hardwood removed for floor repairs:
Note that the short piece on the extreme right is broken in 3 places. It's also a piece that ends on the log joist at this point.
I replaced the piece above with an old piece of barn wood (the same thickness) that I've had lying around in my wood scraps for probably over 6 years. I never thought it would get used, but voila!
In the basement, since I had NO SUPPORT left for the ends of these boards, I decided to add some nice (overkill) pieces of wood. I used old 2x4s (the *real* ones that are actually 2" x 3 3/4"). These were nailed to both log beams and to each other.
In the photo, A are the new support braces, B shows where the floor used to finish. It looks like they carved the log beams farther to move the stairs (or maybe just to get more head room at the bottom of the basement stairs). C is an old length of galvanized pipe that goes to my exterior hose. It's in a bad spot, and you almost bash your head on it each time you go down stairs. I will eventually change it to copper, and move it back.
It seems like normal construction practice (of the time) to simply chop a hole in the floor at any convenient location, and not support the remaining floor planks. This is one of these, where I will be adding a brace to support the ends of the barn boards that hold-up the floor (hardwood) above. Pretty much all the floor grates are cut like this.
As a side note, this is one of the last vents left to fix, and it's the one for the office (which I might be entirely changing (details later), but this is pretty much exactly how they had hooked up the heating vent in the kitchen when I first bought the house. I never took a photo of it, but it was basically this.
Lastly, I built a new temporary step to regain use of the stairs. It's NOT the best setup, since this one is high and awkward, but I'll hopefully be redoing the stairs soon-ish (in the next year). You can see the installed door casing on the living room door, which I can now paint, and cut to length once I have my stair stringers ready to go in.