I guess somebody lost the original parts. When Ruger does the conversion they always return the original parts. They did on mine.
However, after shooting the gun for several years after the conversion, I couldn't stand the action. It just didn't feel right and wasn't as good as the original parts were. So, I took it in to my local gunsmith and asked him to work on it. He said no. He told me that the conversion parts did not respond well to tinkering. He told me to simply convert it back since I had the original parts. So, I had him do it. He did some work on the action at the same time.
My 3-screw is back to it's original configuration, improved, has been for a long time now, and I still love it.
The only regret I have is what I had done to the barrel.:roll: It was originally a 6.5". Years ago I wanted a 4.625, couldn't afford another gun, so I had this one lopped off. The gunsmith did a real nice job on it, but now it's not original. I still love the gun, but wish I hadn't done that now.
But, back to subject at hand. If you can find the owner who originally had the conversion done, he might still have the original parts.
Good Luck!