I am assuming that you are referring to a Ruger MKII Pistol. I have scoped one in the past. After looking at all of the options I decided that the best way was to go to my gunsmith and have him drill and tap it for a Weaver style rail. It ended up costing about $30 for the holes and the rail, which was cheaper than any of the other types of mounts that I could buy local or order and pay freight on. It is also probably a more sturdy mounting system than most of the other types.
Sixgun