I am in agreement with PS on the font match between the receiver and cover.
I've purposely made the cover photo larger.
There are also 1949 dated covers stamped with EM prefixes, sans serif 1's with receivers stamped to match.
Curiously this 1950 dated EM spiker has a serif-ed "1" that falls chronologically between 1949 EM guns with the sans serif 1's.
Which suggests the possibility that the 1949 EM series may not be related to a possible 1950 EM serial run. If the EM run in 1950 did in fact include cruciform bayos, it would have to be a very early run... possibly the first serial prefix pair of 1950.
The stock is odd-- being cut for a spike so late in the Soviet production run. In its favor is the fact that it hasn't been given the faked Westrifle date, arsenal and serial stamps.
But was the bayo channel arsenal modified or humped by westrifle along with the bayo? Here, again, the absence of the humped Westrifle stock stamps suggests (to me, at least), that the bayo channel is an authentic arsenal mod.
To carry that a bit further, I would guess that the arsenal didn't upgrade to the new standard blade bayo often seen on 49 refurbs because the rifle was refurbed for commercial export purposes and not intended for military re-issue...
That day in the refurb factory would have gone something like: "Hey, Vlad, spike bayonetko eez een wary good condeeshon. Tell, Nikita to modify stocko for spike."