Someone may have put S&W grips on that gun, but take another look; I will bet they don't really say "S&W".
S&W NEVER marked a barrel with the legend ".38 LONG" anything. They did mark some early M&P's "For .38 S&W Special and U.S. Service Cartridge." The "U.S. Service Cartridge" is what we call the .38 Long Colt, but the S&W guns did not say that. Other than that, they never made a gun specifically for the .38 Colt cartridge, short or long.
That gun is almost certainly a Spanish copy of the S&W on the outside but with a different mechanism. They were imported by the ton in the 1920's and 1930's. Some were of fair quality, but most were made of cheap cast iron ("pot metal"). I have seen several blown up with normal loads.
I strongly recommend against shooting the gun before having it inspected by a gunsmith or some knowledgeable person.
Value of one of those Spanish guns is negligible except maybe for a deactivated display. One dealer in the area decided to convert a couple into blank guns for starter pistols for the local high school. One blew on the first shot with a blank; the school declined to use the other.
If you can copy the Spanish markings, we can probably translate them.
Jim