I have a 5.6 Winchester that is thought to be original. In the 5.6 run the rear sights could be either a type 1 flip or a type3 adjustable. I would think that by the 5.7 run they were all adjustable sights? You might be looking at the original factory rear sight?
I have three carbines two are original (a 5.6 Win and a 5.4 Inland) as built. all have the adjustable rear sights. All of these sights are centered on the receiver and all shoot exactly to point of aim at 100 yds. The one that is most accurate is my NPM with original IBM Corp barrel and added type 2 rear sight. Before I started taking things off or knocking sights from side to side, I'd check the barrel index and the barrel for straightness. My point is that the upgrades done to these weapons should be looked at as improvements and they should be somewhat centered. That is a very cool looking beautifully patinaed carbine. I'd be very reluctant to change anything except what it takes to make it shoot straight.