Maybe "clamp" the gun/stripper in some kind of fixture with vertical jaws, and then measure from each jaw to the center. When equal from each side, you should be top dead center. Never tried it. Just my brainstorm.
Get some small scope levels put one on the receiver and match that with one where you plan to mount the front sight, mark dead center level drill and mount.
Maybe something like this.
Is the air stripper steel?Have a gunsmith “sweat” the front sight on for you.
Something like the picture I posted is easy to make!We did things like that for Wood working on chairs and Stair rails.Table saw and a drill press is all you need.
Leave it loose until you get to the point of shooting. Set the rear sight centered and the front to what looks about right. Shoot a group and see which way it needs to go. Get it close then lock it down. Now fine tune with the rear. Just another suggestion. Dave