Hi folks. I could use some help. I have the opportunity to buy an old Colt Python, .357 chamber, 6" barrel, nickel finish from a client of mine. Neither of us really know what it's worth, but we've both got a loose idea. It has turn marks on the cylinder but otherwise looks pristine. It comes with the box, which is old. Based on the other guns in his father's collection it sat in the box for who knows how long. The predicament is that the serial number doesn't seem to match up to the charts online or Colt's lookup feature. S/N is K42***. The model is I3661. I imagine someone here can help??