LLMs actually do a very fine job of understanding the "mindset" embodied in historical sources, because historical documents themselves are a valuable source of highly diverse LLM training data. You can easily point pretty much any model to any random historical text, no matter how obscure (probably not an archival log entry, though) and ask "what is this text about in modern language, how might it be of interest or relevant today and what points would be considered especially outdated?" you will generally get very helpful answers. Even the thinking output is instructive.