The adjustable "express sight" that came on my M70 stainless was the adjustable version of the sight sold by New England Custom Guns. NECG also sold and probably still sells a proper replacement single standing leaf express sight that screwed directly in place of the factory sight. You will have to sight in the NECG replacement sight with a file.

Also somebody in Washington state used to make a copy of a pre '64 Winchester M70 African rear sight which was a screw adjustable express sight.

Richard