I bought a used Benelli M1 Tactical that came equipped with factory rifle sights. I would like to replace them with tritium ghost ring sights. I know that Benelli makes factory GRNS, but how do they mount? Will it be necessary to drill & tap the receiver? Any help is appreciated. Also, I am trying to get a copy of the owner's manual but I need Benelli's phone number. I couldn't find it on their web site and their email form is not working. Thanks.