When Russian organizations use calques of their original names as English "self-descriptions" because of lack of command of English by their management, we'd rather expose their illiteracy than correct them
One should be better off with "chemical equipment plant" even though Russian plants of the kind in question specialize in equipment used in process engineering (valves, reactors) rather than in chemical labs (lasers, flasks)
Reasons aside, you simply misread the context
It's about history documents, not business entities: just химических заводов (without proper names), no matter what they might call themselves in English
But might they in 1942? Are you serious?
So, your reasoning misses the whole point of it
For the meaning of техников-механиков, look at the web pages of some Russian vocational colleges whose names are cognate with the term in question:
Омский химико-механический (ХМ) колледж
http://oxmk.ru/index.php?option=com_content&task=view&id=9&I...Краснозаводский ХМ колледж
http://web.tsinet.ru:1080/~khmk/works.htmЕкатеринбургский ХМ техникум
http://www.exmt.narod.ru/Spec.htmВладимирский ХМ колледж
http://www.vxmk33.ru/publ/spec/specialnosti/18