The M19 comes in blued steel or nickel plated. The M66 is basically the same gun as the M19, but in stainless steel. The M66 also comes in a square butt, which is how you usually think of a revolver, and those have either 4', 6', or 8-3/8' barrels.
Since your gun has a 2-1/2' barrel it is also a 'round butt' frame with a smaller grip to make the gun more concealable. I say early 1982 because later the same year, serial numbers went to a 3 letter prefix on all S&W revolvers. The -2 change eliminated the pinned barrel and recessed charge holes in the cylinder. The Model 66 was initially released in 1970. The -2 after M66 in the model number indicates the second engineering change, which occurred in 1982 and lasted until 1986 when the -3 was released. As said, the 241Kxxx is the SN and that dates the gun to early 1982.
