I have sold several of those scopes and usually drilled the existing guide myself. simply take the rear screw out of the ARTII mount, tightnen the front one and use a transfer punch of the correct size to mark your drill spot. then you can remove the guide and drill it. i have heated the guide in a small oven to make drilling easier and also used a diamond drill to do a couple. GI chargers are really hard, aftermarkets were easy to drill.