Mike,
I was looking through some older posts and found your posting about your 45/70 and a scope mount for it. How did you get along with it? I have used Leupold pistol mounts with the Leupold rings that twist in, It works well but you have to drill and tap at least two holes in the top rib. I have also been machining a couple of mounting blocks from material I bought from Brownells made by a company called the Moulds Co. I usually notch the rib for them and have them welded on before installing the rib. I did just finish up a 12 gauge slug gun though, that I notched the rib after installation and put two alien head screws in to hold them down, then used Leupold lever set QD rings on with them and that worked out very well. The iron sights can still be seen when the scope is off but with the mounts still in place. Good luck with your project and with your eyesight! Bob