The serial number is 7304xx. (Many people online will omit the last couple of digits of a gun's serial for security and privacy reasons.) The definitive location of the serial number of most S&W revolvers is on the butt of the grip frame, although a few prewar small-caliber revolvers with oversize target stocks (i.e. grips) had the serial number on the front of the grip frame instead. The number visible inside the yoke cut- the part of the frame that is visible when the cylinder is open- is commonly an assembly number that was used at the factory for assembly purposes, but became meaningless after the gun was shipped.
Given the serial number and the absence of a locking lug at the front of the ejector rod, i believe that this is an early WWII vintage .38/200 British Service Revolver, which would originally have been chambered in .38 S&W but may have had its chambers lengthened to accept .38 Special when it was re-imported. The barrel has been cut, the stocks are aftermarket, and the gun has been refinished with nickel plating; the original finish was probably blued on an early gun like this. These types of modifications were commonly done to these guns to increase their market appeal when they were resold.
More info here:
http://thefiringline.com/forums/showthread.php?t=497657