Check out the cutoff-- it appears to have some weld on it. I would look closely at the the receiver around the cutoff to make sure this wasn't a recovered drill rifle. Could be just the cutoff was from a drill rifle. If it was a drill rifle the 1500 would be way high of course.
After looking at the 5th photo again, you can see the area right below the rear sight and above the cutoff has been machined out to eliminate the weld. I would say this definitely was a drill rifle.