Looks like a really nice sidelock drilling would like to see more pics of it. My pre -war drillings have 2.5" or 65mm chambers so I haven't been able to shoot slugs until this 2.5" product from Brenneke was released. I have been using it with good success. Have you tested it?
Are your scope bases the Akah type slide on or claw?
http://www.brennekeusa.com/cms/brenneke16.html