Are you asking if a Ruger Mark III grip frame will accept a Ruger Mark II upper? If you are mating a steel upper to a steel lower, yes. You will need to use Ruger Mark III magazines then, or you could add the Ruger Mark II magazine latch to the bottom of the Ruger Mark III grip frame and then plug the hole for the Ruger Mark III magazine latch/release. I would prefer using the Ruger Mark III magazine release as that's where Ruger should have put the dang thing back in 1949.
