An outstanding example of what I believe is an "overrun" from the special ordered 5" Combat Masterpiece for the Missouri State Highway Patrol . . . congratulations! They are few in number and not very often seen in the condition of yours.
From our research, the highest s/n of those shipped directly to the MSHP is K157676 but I have recorded s/n's in the K205XXX series that shipped to stocking dealers that had an affinity for special runs &/or non-catalogued barrel lengths. For example K205342 shipped to a Florida S&W dealer and K205385 shipped to a dealer in Los Angeles.
I am aware of one other example that shipped with a target hammer but only a factory letter will tell for yours. Whether the target hammer is original or not you'll find that 5" CM an outstanding handling and shooting revolver!
Russ
P.S. If you're planning to come to the big Tulsa show this weekend I hope you can join us for the Southwest Bunch gathering Saturday evening and bring your 5" for show & tell.
http://smith-wessonforum.com/lounge/602886-southwest-bunch-barbecue-fall-2019-a.html?highlight=Tulsa
I know of an example of an ISP 5" K-38 (heavy barrel version of yours) that will be there! Feel free to call my cell for directions (573-465-1870)