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This particular carbine is a '54 Izhevsk Russian SKS45. From the photos I can tell that it is a CAI import (due to the transliteration of the Cyrillic letters in the S/N which was a CAI specific thing). The mismatching magazine with the lined out original S/N and EP'd correct number indicates that this gun was refurbished prior to import into the US. Looks to be in relatively decent shape for being an almost 70 year old firearm!
If it had been as-issued, you'd likely have a $1200 to $1500 carbine on your hands there as they are quite desirable (though not as tough to find as 1953 Izhevsks are). These '54 refurbs are still desirable to collectors wanting any Izhevsk in their collection and usually fetch a pretty healthy premium over an equal condition Tula. As it currently sits, you might be able to pull $900 in a hotly contested auction (maybe), but I'd say $750 is probably the floor for an Izhevsk in this condition these days. If the stock cartouche is correct and the S/N is matching you may pull another $100 or so vs. if it has a generic refurbished stock.
The other carbine you have may or may not be this one's equal but we would need photos of it to verify for certain.