Well first off the serial number is quite different from Tula manufactured rifles, why is that?
Second what are the production numbers roughly on these? (Or at least in comparison to Tula)
Third aside from the dust cover markings and SN is there anything else different from other Russians?
Like Boris said, nobody truly knows why the S/N format changed. It's interesting, because Ishevsk production of Mosin Nagants, PMs, SVTs, AKs, etc. generally seem to follow the standard dual Cyrillic + up to 4 digit serial format (at least I have not run across any oddball S/N variations in my admittedly limited experience with those other weapons). Why the '54 SKS45s were so very different in format when the '53 Ishevsk SKS45s were pretty 'standard' is one of those head scratchers that will probably never be solved. It seems likely that the Soviets were advancing and/or experimenting a bit with the serialization, but whatever format they came up with didn't seem to stick. It's also interesting that by 1956, we start to see letter year code suffixes pop up on firearms (letter codes had been on cartridges as early as 1952).
True quantity built is another thing that may truly never be known. There have been guesses from Russian sources, something like 2 to 3 million seems to ring a bell but I honestly don't remember and don't have time to look it up right now (one of the more knowledgable members may be able to chime in here).
Based on the SKS45 database we have, here's the rundown of years/arsenal that I'm currently seeing (note that this list may be skewed a bit by the more rare variants getting posted a bit more often than say your run of the mill 1953 refurb):
1949: 55 (4.7%)
1950: 80 (6.8%)
1951: 128 (10.9%)
1952: 106 (9.0%)
1953: 85 (7.2)
1954: 263 (22.4%)
1955: 28 (2.4%)
1956: 94 (8.0%)
1957: 130 (11.1%)
1958: 84 (7.2%)
1953 Ishevsk: 27 (2.3%)
1954 Ishevsk: 90 (7.7%)
Total Tula: 1053 (90%)
Total Ishevsk: 117 (10%)
Total dated carbines in database: 1170 (100%)
Uncertain / Unable to 100% accurately date: 389
Total records in database: 1559
There is nothing mechanically different in an Ishevsk built SKS45 vs a Tula built one. The acceptance stamps are a bit different and the Ishevsk font is immediately identifiable if you've seen enough examples.
Here's the little sister to your carbine:
And here are some of the Ishevsk specific acceptance stamps: