Hello all. I bought a Colt from an Auction site that was listed as a Trooper MK III. Upon arrival and inspection, I think it might not be the MK III model. Barrel is marked "Trooper 357" and below that "357 magnum CTG". Has a service type hammer, not the wide one. Frame is marked 536XX as is the crane. Also has a "D" marked inside the crane. Do I have a Tropper or a MK III? I'm guessing production in the mid 60's. Which frame size is it? Price was right, whichever it is. Many thanks.