Who Case: 433
The Cavalier Tail wasn't developed by TransFlorida/Cavalier.
It 1st appeared on a P-51B late in WWII as North American worked to improve Very High Speed Stability on the Mustang. The Triangle Dorsal Fillet was a previous improvement incorporated.
NACA incorporated the Tall Tail Mod on a Fleet of P-51s used for R&D High Speed Research. Was used as a flying Wind Tunnel by bolting Test Items to the top of the wing over the Gun Bay. This area had alum plates shaped and bolted onto the top of the wing over the gun bay. At A/C speed of Mach .8-.82 the airflow over that part of the upper wing would go Supersonic. The Tall Tail helped with stability at the very high speeds.
The NACA P-51s were sold surplus in 1958 IIRC. Lindsey ended up with one and copied the tall tall mod as an upsale item. That Airframe was the 4th P-51D-5 produced and was kept by NAA for developement work. It ended up with NACA.
There are 2 othe NACA P-51D survivors I know of. One is also flying up in Idaho. The other ended up with Mike Couches and today is in storage with his son.
This who case may then be one of these I mentioned. Of them, two went to Civil Buyers in the late 50s. The one in Idaho was displayed at Reading Airport and then Pittsburgh before being acquired in a trade in the early 90s and restored.