I’ve just found this thread and searched around to see what I could dig up. Here are my thoughts:
As far as I can tell, just by looking at it, “off set themselfs from the tenements of known reality” is literally telling us to find the word themselfs, in something that can be called the tenements of known reality, then use a neighboring word. While themselfs has been interpreted as a misspelling, it is also the archaic version of the word, quite commonly used in this form in the books google threw at me, from the 17th to 19th century. The problem is, there are way too many books, and I have no idea which to look at.
The other thing is, that the tenements of known reality could refer to a real life building, which is in accordance with offseting yourself, or to be more precise, setting off yourself. This aspect of “off set themselves”, meaning to set off, physically, should also be investigated. The question, again, is what tenements to look for? What country even?