The “hand engraved” electopenciled numbers you observed are likely the Yugoslavian-applied assembly numbers found on just a few components that they needed to keep together prior to applying the serial numbers.
If the previous owner didn’t put a top coat of BLO over the stain you might be able to lighten it up a bit by rubbing down with mineral spirits. You aren’t going to get a lot out as wood stain tends to, well, stain the wood, it’s tightly bound. Finish up with a Ballistol rub down.
I wouldn’t worry about shooting it. I guess if the bolt face and gas piston are pristine, and you had other SKSs to shoot, it could be set aside.