Welcome to the files!
You have what we at SKS-Files typically call a ‘Russian Sneak’ there. The import stamp should be either IO out of Monroe or Palm Bay, or TGI out of Knoxville, TN. These are Albanian stored Russian SKS45 carbines that were brought in with a batch of legal Chinese type 56s. The sorting process was not done well and these Russian guns which are not currently importable due to the joint signed voluntary restraint agreement (VRA) were ‘inadvertently’ imported. ATF finally caught on to this after the fact and confiscated and destroyed the remnants of whatever sneaks were left at the importers waiting to be sold to retailers.
Most of the sneaks that turned up have either mismatched (blank Russian or Chinese) receiver covers or are ‘56-‘58 letter guns with inherent blank covers. This one is interesting in that it’s a ‘matching’ cover but it’s not original to that carbine. The carbine is a ‘53 thru ‘55 Tula based on the round front portion of the receiver & the S/N font. Those carbines all had arsenal stamps with years on the original receiver cover. The ‘diver down’ stamp on top of the receiver cover corresponds to the 1st GRAU and is a good indication of the refurbishment of the carbine in the Soviet Union before it was shipped to Albania in the 60’s. The /12\ on the receiver is also a likely refurbishment stamp.