Nice score! I think the sum of the parts is well worth more than what you paid for it (I was watching that auction, but didn't have any "play" money). I agree, and think the number was added by a previous owner, trying to "match" it up. The wrist numbers are too crisp, and you can see the round shank of the stamp. We have similar number stamps at work, and when we stamp aluminum too hard, it leaves that same tell-tale deep number with a round halo around it.
Still, and nice rifle with nice parts!