If you're going to build 'Cripes A' Mighty 3rd', use the 'early production' kit (#3205)... this Mustang was a block-5 production bird and did not leave the factory with the fin fillet, although it was probably fitted in the field at some point.
P-51D 44-13321, 'Cripes A' Mighty 3rd', 487th FS
Little Friends.co.uk
If you're going to do Preddy's last Mustang, named simply 'Cripes A' Mighty' use kit #3201... that ship was a block-15 bird and was built with the fillet.
P-51D 44-14906, 'Cripes A' Mighty, 328th FS
Little Friends.co.uk
Of course, if it were me, I'd wait for a new kit from Hasegagme... but that's just me...
Fade to Black...