Resp:
I know this question deals with post war P-51s, but you may have an answer. I have seen at least two P-51D with extended 'vertical stabilizers' at Air Shows. These are much taller than the 14'8" stabilizer on factory Mustangs. What, if any, advantages does a taller one provide?
NavalWarrior,
IIRC the tail cap was added to the D models starting with the Cavalier modded aircraft (export post WW2). Most I believe were went to South/ Latin America, with some of those actually returning to the states eventually. I have also seen some newer restorations adopting the taller cap without having been a Cavalier plane.
Cheers,
Biff