Howdy again
Nice that you have provided more photos.
If you had mentioned it had Spain stamped on the frame in the first place this whole conversation would have ended very quickly.
Smith and Wesson never used a V shaped hammer spring like that. Never, since 1857. Always a 'leaf' style hammer spring.
Colts, on the other hand, always used a V shaped hammer spring. Smith and Wesson on the left, Colt on the right.
As I mentioned before, with a Smith and Wesson, numbers stamped on the frame under the yoke (crane) are assembly numbers, not serial numbers. As the revolver went through various assembly processes, different parts went to different departments for more work, such as fitting or finishing. Assembly numbers were stamped on the parts so they could be married up again to the same frame during final assembly.
Smith and Wesson never stamped assembly numbers on the yoke in that position. You can see in this photo where the assembly number on the yoke was always stamped.
Notice there is no Rebound Slide in the Spanish revolver. Ever since 1905 S&W revolvers have always used the Rebound Slide to return the trigger to the forward position. The Rebound Slide is the shiny part below the hammer in this photo. The hammer block has been removed for clarity in this photo, it would be riding on the pin in the Rebound Slide. It is more complicated and therefor more expensive to put a Rebound Slide into a revolver, but it makes for a better double action trigger pull. Until the fairly recent change over to frame mounted firing pins, Centerfire S&W revolvers always had the firing pin (S&W actually calls it the 'hammer nose") mounted to the hammer with a rivet. This allows the firing pin to pivot up and down slightly. Some of the larger Smiths actually had a small spring in the hammer, to reposition the firing pin, but with most it can freely rotate a few degrees.
That is clearly not a Smith and Wesson Side plate. I suspect all that metal was removed to clear the V spring. This is a S&W Side Plate. Notice the assembly number stamped in recess for the hand. The hammer block has been positioned in the groove it rides in when the revolver is assembled.
Curious what makes you think your barrel is from 1951. As I mentioned earlier, I have a K frame S&W 38 Military and Police with a serial number 1180XX that shipped in 1908. That is reasonably close to your SN. As I said, S&W revolvers from this period had the SN stamped on the underside of the barrel and the underside of the extractor star, as well as the SN of record on the bottom of the butt. Also, the appearance of S&W markings varied over time. This is the caliber marking on the barrel of a 32-20 Hand Ejector that shipped in 1916. Notice the similarity to the caliber marking on your revolver, particularly the marks at each end of the legend.
This is the caliber marking on the barrel of a K-38 that shipped in 1950. Very different than the caliber marking on your barrel.