Re: Help identifying Spanish revolver with pics
Spanish guns of that era and later often copied foreign guns outwardly, but were modified internally to better suit the Spanish "cottage industry" manufacturing process, which was based on hand work, not machines. I doubt very much that any S&W parts would work in that gun or could be made to work.
Frankly, the gun is old, was not of high quality to begin with, and is not worth spending money on. Consider it as a connection with your grandfather and a piece of family history and give it an honorable retirement on the wall.