That would seem to be a super buy. Three other 127xxx carbines are known, but NO 128xxx or 129xxx. Then there are a few in the 130-131-133xxx range, and that's it. The major group is 118-120xxx.

The stock cannot be altered from another model, so it is real. The only "issue" is that the rear sight leaf and slide are from a rifle. I didn't like the front sight until you clarified that the photo was no good. But, if it were faked with malice, the price would be around $3000, so you are still OK, and can well afford to fix the sight, though it will cost as much as the gun. Congratulations.