Most of the Mustangs that served in the Korean War were those manufactured around the spring and summer of 1945, too late for service in WWII, and were pulled out of storage (as Stiz mentions). During this time, ANG units still used a lot of P-51D's, but some units were also equipped with many P-51H models. I'm not aware of any P-51H's actually being used other than state-side. Following the introduction of the USAF in 1947, the P for pursuit designation was dropped, and all P-51D's were then referred to as F-51D's. Most of the the examples that served in the Korean War seem to be P-51D-25-NA and P-51D-30-NA type examples. By the time of the Korean War, a number of technical orders had been issued for the P-51D/F-51D, even in the years following the end of WWII, which resulted in numerous changes that did not occur on Mustangs during WWII, and with all of the technical orders/upgrades that had been issued, there were no longer as many differences in one F-51D to another (as there were while the P-51D was continuing to be developed throughout the last year and half of WWII), with all of them becoming more standardized. By the time of the Korean War, looking into the cockpit of an F-51D, you would have seen that the entire cockpit was painted black instead of interior green (or at least everywhere that could be reached), the K-14 gunsight would be updated to the latest mods/variant of the time, and the radio sets were different, resulting in a different look both in the controls along the right-hand side of the cockpit, as well as of course the equipment mounted behind the seat/armor plate. They would have all had the tail warning radar set installed, as well as the rocket control system/support for rocket launchers, and most, by this time, would have the rocket launchers mounted under the wings at all times (where as, even though rocket-supported Mustangs were being shipped to England as early as January and February of 1945, none were ever opperated in Europe with the rocket launchers installed).
