I have just purchased a Smith and Wesson 629 Magna classic .44 with a 7 1/2" barrel. It does not have 3 holes drilled in the top strap above the cylinder. The barrel looks like it might be designed for a clamp type scope mount, but I haven't had any luck locating one. I would like to avoid drilling the frame if possible, but I can't see well enough to shoot accurately without magnification. Please advise me as to the best course of action. Thanks!