Lets hope that the rifle is not in original condition. It would be a shame to alter a rifle that has survived without alteration for 90 years. If the rear sight and rear sight spring are removed, the rear bridge can be flattened, and the charger guide trimmed so that a flat bottomed scope base can be fitted. The receiver ring isn't quite cylindrical around the top, so whatever base is used will need to be fitted. You will need to have a pair of bases that can be altered to work - - or a bridge mount adapted. This is going to take time and skill. I would suggest obtaining a separate stripped rear bridge for alteration. Time + skill = $. Once the receiver is drilled, there is no going back, so all the parts should be on hand, and workable before this step. Where to send it? There are a number of talented smiths who are members of this board. If one of them sees your post, and is interested in this job, I'm sure you will get a PM.