ART scope mounting
Original GI M21 ART II scope mounts were installed on the standard GI clip guide which was drilled ant tapped for the second screw. Because of the variations in commercial receivers, each guide must be D&T on a individual basis to insure a proper fit. Pre drilled guides won't always work.
I offer this service for military M21 mounts. Keep in mind that the clip guide is a hardened part and requires special tooling to drill and tap.
The replacement mount that Leatherwood used for commercail sales scopes had a floating sleeve that allowed the rear screw to center properly. The last I heard, Leatherwood no longer offers this part.