These TF-51D's have the taller tail fin cap added atop a stock P-51D tail (no H-model tail/parts involved at all). Around 1944/45, the NACA (forerunner to NASA), working with North American Aviation, designed and produced a taller cap at the tip of the vertical tail fin for the high-speed test P-51D's (and B), which made the vertical fin taller and allowed the aircraft to be more stable in yaw in high-speed dives. One of these NACA P-51D's (NACA 108/44-13257), with the extended tail fin cap, later became the Trans-Florida Aviation prototype Cavalier Mustang in the late 60's. Trans-Florida Aviation liked the NACA taller tail fin cap and copied them and used them on their Cavalier Mustangs (three of which were a combination TEMCO TF-51D, with the extended dual-control cockpit and with the Cavalier-addition of the NACA tail fin cap - which the earlier TEMCO TF-51D's never had). The two TF-51D's seen in this video, operated by Stallion-51, are both non-original TF-51D's, and only became TF-51D's when the airframes were rebuilt/restored (80's and 90's). As with most of these modern TF-51D's, they are modeled after a combination of the original 1950's TEMCO TF-51D's and the few, later, 60's-era Cavalier TF-51D's.