I’m not sure what your ‘code’ down in the Excited States calls for in terms of the vent or the romex, although I suspect that the romex should be covered to prevent damage and probably set back from the heat duct.
I see a lot of houses in my area that are 150+ years old. MOST of them have settlement issues as you have described. The question is; " Is this a recent development or has it been going on for the last 100 years?". All houses subside eventually and in a house this age it is usually pretty easy to discover what is causing it and what if anything can be done to arrest the process.
Some purchasers look on these subsidences as a ‘feature’ of the house ( I guess they like the fact that if they drop something it automatically roles to the middle of the house!!) Others view it a s a warning that the entire structure is about to collapse and possibly drag the neighbours house in with it.
The truth lies somewhere in between.
The cause, in my experience is usually a poorly supported main beam in the basement which has deflected over the years. In fairness to the builders of the 1800 of this area, they usually used a massive log ( probably cut on site) squared it by hand and placed it on supports as a main beam. I often find that someone has removed some or all of the supports over the years and the result is a deflected beam. Look for dry rot or excessive humidity too as both can cause a big beam to sag.