The easy answer is the gun was manufactured in 1958, the first full year that Model numbers were used for the Masterpiece line. Check the yoke and frame when you have the cylinder open and look for a model number stamped in the inside of the frame.
The not so easy answer is valuing a gun that has been butchered if one is looking for a collector gun. Some members put the aesthetics of a nice set of stocks over the actual value of the gun. The gun has no collector value since such a large chunk of it is gone. The stocks have some value, but I would not put Fuzzy Farrants at the top of any list of collector stocks. I would pass on this gun at any price because of the alterations and because I already own a nice example.
As for factory stocks, actually S&W diamond Target stocks would fit just fine on the gun, covering the cut butt-frame and bringing the gun back to what it could have looked like when it left the factory. If I owned the gun, I would find a set to put on the gun, then sell the Farrants to offset the cost. Magna stocks would not work on your gun. One of the nicest looking revolver S&W ever made was the K Masterpiece with target stocks.