Is there a glossary to the jargon he uses in this post (M.41, M.42)?

Without looking at the post... I'd say that M.41 is the dark, troubled and uncertain time that we live in, and M.42 is prophesized to be the Time of Ending itself, when either the God-Emperor will return in His full glory to lead mankind anew, or the Imperium will be torn apart by Chaos and the ravening xenos, never to be rebuilt. So there.

Edit: I looked at the post, but I still prefer the WH40k interpretation, since it suits them neo-reactionaries better!