Unfortunately, used Rugers that have been converted often lack the original parts. Either they were misplaced or sold by the owner, as they do bring a rather handsome price. And finding these is somewhat of an ordeal. I bought two .357 Magnum Blackhawks and it took more than a little effort to find the parts to put my guns back in original shape.
I've had three three screw models that had been converted. One was a Super Blackhawk, and the conversion parts made it an awful mess actionwise. I have stockpiled a few parts for un-converting any future purchases.